SCOTUS Reports

Tag: IRS Audit

  • Jones v. Commissioner, 97 T.C. 7 (1991): Exclusionary Rule Not Applied in Civil Tax Cases

    Jones v. Commissioner, 97 T. C. 7 (1991)

    The exclusionary rule will not be applied in civil tax cases to suppress evidence obtained through alleged constitutional violations during a criminal investigation conducted under the guise of a civil examination.

    Summary

    The Joneses alleged that IRS agents conducted a criminal investigation under the guise of a civil audit, violating their Fourth Amendment rights. The Tax Court held that even if such violations occurred, the exclusionary rule would not be applied in this civil tax case. The court reasoned that the exclusionary rule’s deterrent effect had already been served through a plea agreement in a related criminal case, and its application would impose a high cost on the civil tax system. The decision underscores the limited applicability of the exclusionary rule in civil contexts and emphasizes the importance of honest conduct by IRS agents.

    Facts

    James and Grace Jones, along with their company Ken’s Audio Specialties, were under IRS scrutiny for tax deficiencies from 1980 to 1985. IRS Special Agents Schwab and Cunard, after reviewing the Joneses’ lavish lifestyle against their reported income, referred the case to the Examination Division for a civil audit. Revenue Agent Waldrep conducted the audit but allegedly collaborated with the Criminal Investigation Division (CID), leading to the Joneses’ cooperation under the belief it was a civil matter. The Joneses later pleaded guilty to criminal tax charges, and subsequently moved to suppress the evidence obtained during the civil audit in their civil tax case, alleging Fourth Amendment violations.

    Procedural History

    The IRS issued notices of deficiency to the Joneses and their company for the years in question. The Joneses filed petitions with the U. S. Tax Court, challenging the deficiencies and moving to suppress evidence obtained during the audit, claiming constitutional rights violations. The Tax Court consolidated the cases for the purpose of deciding the suppression motion.

    Issue(s)

    1. Whether evidence obtained through alleged constitutional violations during a criminal investigation conducted under the guise of a civil audit should be suppressed in a civil tax case?

    Holding

    1. No, because even if constitutional rights were violated, the exclusionary rule will not be employed in the setting of this civil tax case due to the limited deterrent effect and high cost to the civil tax system.

    Court’s Reasoning

    The court analyzed the application of the exclusionary rule in civil cases, noting its primary purpose is deterrence. It cited Supreme Court cases that limited the rule’s use, particularly in civil contexts. The court distinguished this case from criminal cases where the rule might apply, such as United States v. Tweel, due to the civil nature of the proceedings and the lack of direct misrepresentation by IRS agents. The court also considered that the deterrent effect had been achieved through a plea agreement in the related criminal case. The court emphasized that the evidence was obtained for civil tax enforcement, the very purpose it was being used for in this case. Despite finding the IRS agents’ conduct reprehensible, the court declined to apply the exclusionary rule, citing the potential chilling effect on civil examinations and the need for IRS agents to act honestly.

    Practical Implications

    This decision clarifies that the exclusionary rule’s application in civil tax cases is highly limited, even when constitutional rights may have been violated during a related criminal investigation. Practitioners should be aware that evidence obtained through potentially improper means during a civil audit will likely not be suppressed in subsequent civil tax proceedings. The ruling encourages IRS agents to conduct their duties honestly and transparently, as any deceitful practices could lead to sanctions in criminal proceedings. The decision may influence future cases involving allegations of IRS misconduct during audits, emphasizing the distinction between civil and criminal tax enforcement. Later cases may reference Jones to argue against the application of the exclusionary rule in civil contexts.

  • High Adventure Ministries, Inc. v. Commissioner, 79 T.C. 424 (1982): When an Actual Controversy Exists for Declaratory Judgment on Tax-Exempt Status

    High Adventure Ministries, Inc. v. Commissioner, 79 T. C. 424 (1982)

    The Tax Court lacks jurisdiction under Section 7428 to issue a declaratory judgment on an organization’s tax-exempt status unless there is an actual controversy regarding that status.

    Summary

    High Adventure Ministries, a California nonprofit, sought a declaratory judgment from the Tax Court under Section 7428 to affirm its tax-exempt status under Section 501(c)(3), claiming the IRS lacked reasonable cause to audit it. The IRS moved to dismiss for lack of jurisdiction, arguing no determination of exempt status had been made. The court agreed, finding no actual controversy over the organization’s exempt status existed, as the IRS had not yet issued a proposed revocation notice. The court emphasized that Section 7428 jurisdiction requires a concrete dispute over exempt status, not merely over the propriety of an audit.

    Facts

    High Adventure Ministries, Inc. , a California nonprofit corporation, operated a missionary radio station in “Free Lebanon” that was occasionally used by Major Saad Haddad, leading to concerns about political activity. In 1980, the IRS began investigating the organization’s tax-exempt status under Section 501(c)(3) after allegations of political involvement. The IRS sent multiple requests for information, which the organization refused to answer, asserting the audit was politically motivated and lacked reasonable cause. In 1981, the organization sought a declaratory judgment from the Tax Court to affirm its exempt status and challenge the audit’s propriety.

    Procedural History

    The IRS issued a determination letter in 1973 recognizing High Adventure Ministries as a church exempt under Section 501(c)(3). In 1980, the IRS began investigating the organization’s continued qualification for exempt status. After the organization refused to provide requested information, it filed a petition in the Tax Court in 1982 under Section 7428 for a declaratory judgment on its exempt status. The IRS moved to dismiss the petition, arguing the court lacked jurisdiction because no actual controversy existed regarding the organization’s exempt status.

    Issue(s)

    1. Whether the Tax Court has jurisdiction under Section 7428 to issue a declaratory judgment on an organization’s exempt status when the IRS has not yet issued a proposed revocation notice.

    Holding

    1. No, because there is no actual controversy regarding the organization’s exempt status. The court reasoned that the IRS had not yet proposed revocation, and the organization’s dispute was over the audit’s propriety, not its exempt status.

    Court’s Reasoning

    The court applied Section 7428, which authorizes declaratory judgments on an organization’s initial or continuing qualification as tax-exempt, but only in cases of actual controversy. The court cited Maryland Casualty Co. v. Pacific Coal & Oil Co. , 312 U. S. 270 (1941), defining an actual controversy as a substantial dispute of sufficient immediacy and reality. The court found no such controversy existed here, as the IRS had not issued a proposed revocation notice, and the organization’s dispute was with the audit itself, not its exempt status. The court also noted that the organization’s letters to the IRS did not constitute requests for a new determination of exempt status. The court emphasized that it lacked jurisdiction to supervise IRS examinations and that other forums existed for challenging IRS summonses during audits.

    Practical Implications

    This decision clarifies that organizations cannot use Section 7428 to challenge IRS audits before a proposed revocation of exempt status. Practitioners advising tax-exempt organizations should ensure clients understand the distinction between challenging an audit’s propriety and seeking a declaratory judgment on exempt status. Organizations facing audits should comply with information requests to preserve their ability to challenge a proposed revocation if issued. The ruling also highlights the importance of exhausting administrative remedies before seeking judicial review. Subsequent cases like United States v. Coates, 692 F. 2d 629 (9th Cir. 1982), have affirmed that other forums exist for challenging IRS summonses during audits, reinforcing the limited scope of Tax Court jurisdiction under Section 7428.

  • Ballantine v. Commissioner, 70 T.C. 558 (1978): The Effect of IRS Noncompliance with Section 7605(b) on Deficiency Notices

    Ballantine v. Commissioner, 70 T. C. 558 (1978)

    The IRS’s failure to issue a second examination letter under section 7605(b) does not invalidate a notice of deficiency or shift the burden of proof if no second examination occurred.

    Summary

    In Ballantine v. Commissioner, the Tax Court ruled that the IRS’s failure to issue a second examination letter under section 7605(b) did not invalidate the notices of deficiency issued to the taxpayers. The court held that since no second examination took place, there was no violation of section 7605(b). The taxpayers argued that the IRS’s actions were arbitrary and excessive, but the court found that the IRS’s deficiency determinations were based on available information, and thus, the burden of proof remained with the taxpayers. This decision clarifies that the IRS’s noncompliance with section 7605(b) does not automatically void a notice of deficiency or shift the burden of proof in the absence of a second examination.

    Facts

    Robert A. Ballantine and Inez V. Ballantine, along with their related corporations, were audited by the IRS from August 8, 1975, to February 10, 1977. During the audit, the IRS requested the taxpayers to execute “Slush Fund Affidavits,” which they refused on Fifth Amendment grounds. Subsequently, the IRS sought further access to their books and records, but the taxpayers, advised by counsel, refused to allow further access without a second examination letter under section 7605(b). The IRS issued deficiency notices without further inspection, leading the taxpayers to challenge these notices on the grounds that the IRS violated section 7605(b) by not issuing a second examination letter.

    Procedural History

    The taxpayers filed a petition with the Tax Court challenging the IRS’s deficiency determinations. The IRS moved to strike paragraph 4(e) of the petition, which alleged a violation of section 7605(b), claiming it failed to state a claim upon which relief could be granted. The taxpayers cross-moved to dismiss the case or, alternatively, the IRS’s motion to strike, arguing that the IRS failed to timely move with respect to the petition. The Tax Court heard arguments on both motions and ultimately adopted the opinion of the Special Trial Judge.

    Issue(s)

    1. Whether the IRS’s failure to issue a second examination letter under section 7605(b) renders the notices of deficiency null and void?
    2. Whether the IRS’s failure to issue a second examination letter shifts the burden of proof to the IRS by rendering the deficiency notices arbitrary and excessive?

    Holding

    1. No, because no second examination occurred, and thus, there was no violation of section 7605(b).
    2. No, because the deficiency notices were based on available information and not deemed arbitrary and excessive solely due to the lack of a second examination letter.

    Court’s Reasoning

    The court applied section 7605(b), which limits the IRS to one inspection per taxable year unless the taxpayer requests otherwise or the IRS provides written notice of an additional inspection. The court reasoned that since no second examination took place, there was no violation of section 7605(b). The court cited United States Holding Co. v. Commissioner and Rose v. Commissioner, where similar facts led to the same conclusion. The court also distinguished Reineman v. United States, noting that it involved a second examination without notice, unlike the present case. The court emphasized that the taxpayers’ refusal to allow further inspection did not compel the IRS to issue a second examination letter, and the IRS’s decision to issue deficiency notices based on existing information did not render them arbitrary and excessive. The court also noted that the taxpayers’ claim regarding the second examination letter was intertwined with other allegations of arbitrary and excessive determinations, but striking paragraph 4(e) would not prejudice their case.

    Practical Implications

    This decision clarifies that the IRS’s noncompliance with section 7605(b) does not automatically invalidate a notice of deficiency or shift the burden of proof unless a second examination occurs without proper notification. Attorneys should advise clients that refusing further IRS access to records without a second examination letter does not provide a defense against a notice of deficiency. Practitioners should focus on proving that deficiency notices are arbitrary and excessive based on the information available to the IRS, rather than relying solely on procedural noncompliance. This ruling has been followed in subsequent cases, reinforcing the principle that the IRS’s procedural errors do not necessarily undermine its substantive determinations.

  • Chaum v. Commissioner, 69 T.C. 156 (1977): Burden of Proof in Partnership Loss Deductions

    Chaum v. Commissioner, 69 T. C. 156 (1977)

    The burden of proof to substantiate a partnership loss deduction remains with the taxpayer, even when the IRS’s determination is based on an incomplete audit of the partnership.

    Summary

    In Chaum v. Commissioner, the Tax Court denied the taxpayers’ motion for summary judgment and their motion to shift the burden of proof regarding their claimed partnership loss deduction. The IRS had disallowed the taxpayers’ loss from Plaza Three Development Fund before completing its audit of the partnership’s return. The court held that the IRS’s action was not arbitrary, as it was necessary to protect revenue while allowing the partnership time to respond. The court also reaffirmed that the burden of proving a deduction always lies with the taxpayer, emphasizing the practical need for taxpayers to substantiate their claims even in complex partnership arrangements.

    Facts

    In November 1972, Elliot and Elinor Chaum acquired a limited partnership interest in Plaza Three Development Fund, an oil and gas drilling partnership. In October 1973, the IRS began auditing Plaza’s 1972 return. By April 1976, the audit was not complete, and the IRS issued a notice of deficiency to the Chaums disallowing their claimed partnership loss. The Chaums had refused to extend the statute of limitations, which was set to expire on April 15, 1976. The IRS had not formally adjusted Plaza’s return but had communicated with the partnership about potential issues.

    Procedural History

    The Chaums filed a petition contesting the deficiency notice. They moved for summary judgment and sought a determination that the burden of proof should shift to the IRS. The Tax Court heard arguments and reviewed stipulations of fact from both parties before issuing its decision.

    Issue(s)

    1. Whether the IRS’s disallowance of the Chaums’ partnership loss deduction was proper when the audit of the partnership’s return was incomplete.
    2. Whether the burden of proof should shift to the IRS due to the alleged arbitrariness of the deficiency notice.

    Holding

    1. No, because the IRS’s action was not arbitrary but a reasonable measure to protect revenue while allowing the partnership full opportunity to respond.
    2. No, because the burden of proving a deduction always remains with the taxpayer, and the IRS’s action was not arbitrary or unreasonable.

    Court’s Reasoning

    The court applied the rule that a deficiency notice must meet statutory requirements, which the IRS’s notice did. The court found that the IRS’s action was not arbitrary, as it was necessary to protect revenue while allowing Plaza time to respond to the audit. The court cited cases like Marx v. Commissioner and Roberts v. Commissioner to support its stance that a deficiency notice, even if based on incomplete information, is not void. The court also emphasized that the burden of proof for deductions remains with the taxpayer, as established in Helvering v. Taylor and reaffirmed in cases like Rockwell v. Commissioner. The court noted that the Chaums’ inability to provide more information due to the complexity of the partnership did not shift the burden of proof.

    Practical Implications

    This decision underscores the importance of taxpayers maintaining and presenting substantiation for claimed deductions, particularly in complex partnership scenarios. It clarifies that the IRS can issue deficiency notices based on incomplete audits without being deemed arbitrary, as long as the action is reasonable under the circumstances. Practitioners should advise clients to cooperate fully with IRS audits and be prepared to substantiate their deductions, even if the partnership’s audit is ongoing. The ruling has been cited in later cases to support the principle that the burden of proof for deductions remains with the taxpayer, impacting how similar cases are analyzed and how legal practice in this area proceeds.

  • Stewart v. Commissioner, 66 T.C. 54 (1976): Calculating Fraud Penalty Based on Original Timely Return

    Stewart v. Commissioner, 66 T. C. 54 (1976)

    The fraud penalty under section 6653(b) of the Internal Revenue Code is calculated based on the difference between the correct tax due and the tax shown on the original, timely filed return.

    Summary

    In Stewart v. Commissioner, the U. S. Tax Court upheld the IRS’s method of calculating the fraud penalty under section 6653(b) of the Internal Revenue Code. The case involved Bennie and Dorothy Stewart, who had underreported their income for 1962 and 1963. After an audit began, they paid the additional taxes owed before the IRS issued a notice of deficiency. The court ruled that the fraud penalty should be applied to the difference between the correct tax liability and the tax shown on their original timely returns, not reduced by subsequent payments made after the audit commenced. This decision reinforces the principle that taxpayers cannot avoid fraud penalties by paying additional taxes after fraud is discovered.

    Facts

    Bennie and Dorothy Stewart filed joint federal income tax returns for 1962 and 1963, understating their income and tax liabilities. An IRS audit began in 1966, and in 1970, the Stewarts paid the additional taxes owed for those years. In 1972, the IRS assessed these payments and issued a notice of deficiency, imposing fraud penalties under section 6653(b) based on the difference between the correct tax liability and the tax reported on the original returns.

    Procedural History

    The Stewarts petitioned the U. S. Tax Court after receiving the notice of deficiency. The court reviewed the case, focusing on whether the fraud penalty should be calculated using the tax shown on the original timely returns or the tax paid after the audit began.

    Issue(s)

    1. Whether the fraud penalty under section 6653(b) should be calculated based on the difference between the correct tax liability and the tax shown on the original timely return, or should it account for subsequent payments made after the audit commenced?

    Holding

    1. Yes, because the fraud penalty under section 6653(b) is to be applied to the difference between the correct tax due and the tax shown on the original timely return, not reduced by subsequent payments made after the audit began.

    Court’s Reasoning

    The court reasoned that the fraud penalty under section 6653(b) should be calculated based on the difference between the correct tax liability and the tax shown on the original timely return, consistent with the judicial interpretation of the 1939 and 1954 Codes. The court emphasized that allowing taxpayers to reduce the fraud penalty by paying additional taxes after an audit would undermine the purpose of the penalty. The decision relied on previous case law, such as Papa v. Commissioner and Levinson v. United States, which upheld the same method of calculation. The court also noted that the legislative history of section 6653(b) and section 6211 did not indicate any intent to change the established practice.

    Practical Implications

    This decision clarifies that the fraud penalty is calculated based on the original timely return, not affected by subsequent payments made after an audit begins. Tax practitioners must advise clients that attempting to mitigate fraud penalties by paying additional taxes after an audit is initiated will not be effective. This ruling reinforces the IRS’s ability to enforce fraud penalties and may deter taxpayers from engaging in fraudulent underreporting with the hope of avoiding penalties through later payments. Subsequent cases, such as Papa and Levinson, have followed this precedent, ensuring consistency in the application of fraud penalties.

  • Las Cruces Oil Co., Inc. v. Commissioner, 61 T.C. 127 (1973): Basis of Transferred Assets in Section 351 Transactions

    Las Cruces Oil Co. , Inc. v. Commissioner, 61 T. C. 127 (1973)

    In a Section 351 transfer, the transferee corporation’s basis in the transferred assets should be the actual basis in the hands of the transferor, not the erroneously reported basis on the transferor’s tax returns.

    Summary

    In Las Cruces Oil Co. , Inc. v. Commissioner, the Tax Court ruled that a corporation receiving assets in a tax-free exchange under Section 351 must use the actual basis of those assets, as held by the transferor, rather than the erroneously lower basis reported on the transferor’s tax returns. The case involved a transfer of inventory from partnerships to a corporation, where the partnerships had inadvertently omitted a portion of their inventory from their final returns. The court held that the corporation could use the correct inventory value as its opening basis, emphasizing that errors in the transferor’s tax reporting should be corrected in the year they occurred, not carried forward to affect the transferee’s basis.

    Facts

    Las Cruces Oil Co. , Inc. was formed when two partnerships transferred their assets to it in exchange for stock in a transaction qualifying under Section 351. The partnerships used the accrual method of accounting and had inadvertently omitted $6,739. 72 worth of underground gas and diesel fuel from their closing inventory on their final partnership returns. Las Cruces Oil Co. , Inc. included the correct inventory value in its opening inventory for its first tax year. The IRS challenged this, asserting that Las Cruces should use the lower, erroneous figure reported by the partnerships.

    Procedural History

    The IRS determined deficiencies and additions to Las Cruces Oil Co. , Inc. ‘s federal income taxes for the fiscal years ending June 30, 1969, and June 30, 1970, based on the use of the erroneous inventory figure. Las Cruces Oil Co. , Inc. contested this determination, leading to the case being heard by the Tax Court.

    Issue(s)

    1. Whether, under Section 362(a)(1), a corporation receiving assets tax-free under Section 351 must use as its opening inventory basis the erroneous total reported on the transferor’s final returns or the actual amount of inventory held by the transferor at the time of transfer.

    Holding

    1. No, because Section 362(a)(1) requires the transferee to use the basis of the transferred property as it would be in the hands of the transferor, which is the actual inventory value, not the erroneously reported value.

    Court’s Reasoning

    The Tax Court emphasized that Section 362(a)(1) specifies the transferee’s basis in transferred property should be the same as it would be in the hands of the transferor. The court rejected the IRS’s argument that the erroneously reported inventory figure on the partnerships’ final returns should be used, as this would distort the transferee’s income. The court clarified that errors in inventory reporting should be corrected in the year they occur, not carried forward to affect the transferee’s basis. The court cited previous cases to support the principle that a taxpayer’s basis is not reduced by erroneous deductions in earlier years, and that adjustments for such errors should be made in the year of the mistake. The court also noted that Section 362(a) does not authorize adjustments to the transferee’s tax liabilities to compensate for errors in the transferor’s returns.

    Practical Implications

    This decision reinforces that in Section 351 transactions, the transferee’s basis in transferred assets should reflect the actual basis of those assets in the hands of the transferor, regardless of errors in the transferor’s tax reporting. Legal practitioners must ensure that clients accurately report the basis of assets transferred in such transactions to avoid disputes with the IRS. Businesses engaging in Section 351 transfers should maintain meticulous records of their inventory to prevent similar issues. This ruling may also impact how the IRS audits Section 351 transactions, focusing on the actual basis of transferred assets rather than reported figures. Subsequent cases may cite Las Cruces Oil Co. , Inc. when addressing the proper basis determination in similar tax-free transfers.

  • Harbor Chevrolet Corp. v. Commissioner, 26 T.C. 151 (1956): Estoppel and Unused Excess Profits Tax Credits

    Harbor Chevrolet Corp. v. Commissioner, 26 T.C. 151 (1956)

    The Commissioner of Internal Revenue is not estopped from correcting errors in the application of tax law, even if those errors were initially overlooked by IRS agents in prior years’ audits.

    Summary

    Harbor Chevrolet Corporation sought to carry over an unused excess profits credit from 1944 to 1945. The IRS disallowed this carry-over, leading to a deficiency in the 1945 excess profits tax. Harbor Chevrolet argued that the IRS was estopped from disallowing the carry-over because IRS agents had previously overlooked similar errors in prior years. The Tax Court held that the IRS was not estopped from correcting errors in the application of the tax law, even if those errors were initially overlooked by IRS agents and that the court lacked the power to apply equitable recoupment or order refunds for prior tax years.

    Facts

    Harbor Chevrolet Corporation (the petitioner) sought to carry over an unused excess profits credit adjustment from 1944 to 1945. During reviews of the petitioner’s excess profits tax returns for 1943 and 1944, IRS agents did not question the petitioner’s treatment of unused excess profits credit adjustments. The IRS later determined that the carry-over from 1944 to 1945 was incorrect, resulting in a deficiency for 1945.

    Procedural History

    The Commissioner of Internal Revenue determined a deficiency in Harbor Chevrolet’s excess profits tax for 1945. Harbor Chevrolet petitioned the Tax Court for a redetermination of the deficiency. The Tax Court upheld the Commissioner’s determination.

    Issue(s)

    1. Whether the Commissioner is estopped from disallowing a carry-over of an unused excess profits credit adjustment from 1944 to 1945, where IRS agents had previously overlooked similar errors in prior years’ audits.
    2. Whether the Tax Court has the power to order a refund of tax or a credit of any overpayment of tax for an earlier year against the 1945 tax.
    3. Whether the Tax Court has the power to apply the doctrine of equitable recoupment to offset an overpayment of excess profits tax for 1941 against the deficiency in the 1945 excess profits tax.

    Holding

    1. No, because “an unlawful course of procedure, however prolonged, is not made lawful by acquiescence of the Commissioner.”
    2. No, because the court’s considerations cannot reach section 3801, which governs mitigation of limitations provisions.
    3. No, because the Tax Court lacks the power to apply the doctrine of equitable recoupment.

    Court’s Reasoning

    The court reasoned that the Commissioner is bound to apply section 710(c) of the Code properly in determining the excess profits tax for 1945. The court stated, “The respondent is bound to apply section 710 (c) properly in making his determination of the amount of the excess profits tax for 1945 in accordance with the statute, and if his agents erred in failing to find error in the petitioner’s treatment of the unused excess profits credit adjustments in the excess profits tax returns for 1944 and 1943, the respondent cannot perpetuate errors of either the taxpayer or his agents in determining the amount of the 1945 excess profits tax liability of the petitioner.” The court cited Mt. Vernon Trust Co. v. Commissioner, 75 Fed. (2d) 938, and Commissioner v. Rowan Drilling Co., 130 Fed. (2d) 62, 65, emphasizing that “an unlawful course of procedure, however prolonged, is not made lawful by acquiescence of the Commissioner.” The court also noted it lacked the power to order a refund or apply equitable recoupment, citing Commissioner v. Gooch Milling & Elevator Co., 320 U. S. 418.

    Practical Implications

    This case reinforces the principle that the IRS is not bound by prior errors or omissions in its audits. Taxpayers cannot rely on past oversights by the IRS to justify incorrect tax treatment in subsequent years. The IRS has the authority to correct errors and enforce the tax laws as written, even if it means disallowing deductions or credits that were previously accepted. This case serves as a reminder that taxpayers bear the ultimate responsibility for ensuring the accuracy of their tax returns and that consistency in error does not create a right to continue that error. Taxpayers should proactively ensure compliance rather than relying on potential oversights by the IRS. This principle continues to apply to various areas of tax law, preventing taxpayers from claiming estoppel based on prior IRS inaction.