45 CFR 33.15 - Refunds.
(a) The Secretary shall promptly refund any amounts paid or deducted under this part when:
(1) A debt is waived or otherwise found not owing to the United States; or
(2) The employee's paying agency is directed by administrative or judicial order to refund amount deducted from the employee's current pay.
(b) Unless required or permitted by law or contract, refunds shall not bear interest.