29 CFR 1450.24: Liquidation from final check or recovery from other payment.

(a) If the employee retires or resigns or if his or her employment or period of active duty ends before collection of the debt is completed, offset of the entire remaining balance on the debt may be made from a final payment of any nature, including but not limited to, final salary payment or lump-sum leave due to the employee as of the date of separation.

(b) If the debt cannot be liquidated by offset from a final payment, offset may be made from later payments of any kind due from the United States, including, but not limited to, the Civil Service Retirement and Disability Fund, pursuant to § 1450.11 of this regulation.