26 U.S.C. § 3503 : US Code - Section 3503: Erroneous payments

Search 26 U.S.C. § 3503 : US Code - Section 3503: Erroneous payments

Any tax paid under chapter 21 or 22 by a taxpayer with respect to
any period with respect to which he is not liable to tax under such
chapter shall be credited against the tax, if any, imposed by such
other chapter upon the taxpayer, and the balance, if any, shall be
refunded.