29 CFR 1450.26 - Refunds.
(a) Refunds shall promptly be made when -
(1) A debt is waived or otherwise found not owing to the United States (unless expressly prohibited by statute or regulation); or
(2) The employee's paying agency is directed by an administrative or judicial order to refund amounts deducted from his or her current pay.
(b) Refunds do not bear interest unless required or permitted by law or contract.