26 U.S.C. § 3502: Nondeductibility of taxes in computing taxable income

(a) The taxes imposed by section 3101 of chapter 21, and by sections 3201 and 3211 of chapter 22 shall not be allowed as a deduction to the taxpayer in computing taxable income under subtitle A. (b) The tax deducted and withheld under chapter 24 shall not be allowed as a deduction either to the employer or to the recipient of the income in computing taxable income under subtitle A.