12 CFR §1408.38

1. (a)The regulations contained in this subpart do not preclude an employee from requesting a waiver of an overpayment under 5 U.S.C. 5584 or 8346(b), 10 U.S.C. 2774, 32 U.S.C. 716, or in any way questioning the amount or validity of a debt by submitting a subsequent claim to the General Accounting Office in accordance with the procedures prescribed by the General Accounting Office.
2. (b)These regulations also do not preclude an employee from requesting a waiver pursuant to other statutory provisions pertaining to the particular debts being collected.