5 CFR 831.2104: Eligibility to make deposit.

The following individuals may make deposit for any full period of service performed before the separation on which title to civil service annuity is based:

(a) An employee or Member currently occupying a position subject to subchapter III of chapter 83 of title 5, United States Code, and the survivor(s) of such an employee or Member who dies in service (including a person who was eligible to make a deposit under this paragraph but who failed to make the deposit before separation from service due to administrative error); and

(b) A former employee or Member who was separated with title to an annuity or who retired from a position subject to subchapter III of chapter 83 of title 5, United States Code, after September 8, 1982, and before October 1, 1983, and the survivor(s) of such an employee or Member.