5 CFR §2429.19

Consistent with the exceptions in 5 U.S.C. 7115(b), after the expiration of the one-year period during which an assignment may not be revoked under 5 U.S.C. 7115(a), an employee may initiate the revocation of a previously authorized assignment at any time that the employee chooses. After the expiration of the one-year period of irrevocability under 5 U.S.C. 7115(a), upon receiving an employee's request to revoke a previously authorized dues assignment, an agency must process the revocation request as soon as administratively feasible.