26 U.S.C. § 6514 — Credits or refunds after period of limitation

(a) Credits or refunds after period of limitation A refund of any portion of an internal revenue tax is treated as erroneous and a credit of any such portion is treated as void—
(1) Expiration of period for filing claim If made after the expiration of the period of limitation for filing claim therefor, unless within such period claim was filed; or
(2) Disallowance of claim and expiration of period for filing suit In the case of a claim filed within the proper time and disallowed by the Secretary^*, if the credit or refund was made after the expiration of the period of limitation for filing suit, unless within such period suit was begun by the taxpayer^*.
(3) Recovery of erroneous refunds For procedure by the United States to recover erroneous refunds, see sections 6532(b) and 7405.

(b) Credit after period of limitation Any credit against a liability in respect of any taxable year^* must be void if any payment in respect of such liability would be considered an overpayment under section 6401(a).