(a) (1) An employee or Member may contribute to the Thrift Savings Fund in any pay period, pursuant to an election under subsection (b), an amount not to exceed the maximum percentage of such employee's or Member's basic pay for such pay period allowable under paragraph (2). Contributions under this subsection pursuant to such an election shall, with respect to each pay period for which such election remains in effect, be made in accordance with a program of regular contributions provided in regulations

(a)Participant not employed. The following rules apply to participants who receive a back pay award or other retroactive pay adjustment for a period during which the participant was separated from Government service or was not appointed to a position that is covered by FERS, CSRS, or an equivalent system under which TSP participation is authorized: (1) If the participant is reinstated or retroactively appointed to a hich TSP participation is authorized, immediately upon reinstatement or retroactive