26 U.S.C. § 6406: Prohibition of administrative review of decisions

In the absence of fraud or mistake in mathematical calculation, the findings of fact in and the decision of the Secretary upon the merits of any claim presented under or authorized by the internal revenue laws and the allowance or non-allowance by the Secretary of interest on any credit or refund under the internal revenue laws shall not, except as provided in subchapters C and D of chapter 76 (relating to the Tax Court), be subject to review by any other administrative or accounting officer, employee, or agent of the United States.