5 CFR 837.301 - Coverage.
(a) When annuity terminates on, or is suspended during, reemployment. Retirement coverage under either CSRS or FERS is governed by subpart B of part 831 or subpart A of part 842 of this chapter, as is appropriate.
(b) When annuity continues.
(1) Unless a reemployed FERS annuitant's employment is on an intermittent basis, as an employee subject to another retirement system, or as President, deductions for the Fund shall be made under 5 U.S.C. 8422(a).
(2) A CSRS annuitant is not subject to deductions, unless he or she is serving in an other-than-intermittent status (except as President), is not covered by another retirement system, and elects to have retirement deductions made from his or her pay. Generally, deductions are made no later than the beginning of the first pay period immediately following the date the reemployed annuitant files the election with the employing agency. When the annuitant elects to have deductions made, he or she may not change the election during continuous service with that agency.
(3) The amount of basic pay prior to offset of annuity under § 837.303 of this part is used in computing the amount of deductions. The rate of retirement deductions is that which attaches to the position under the provisions of sections 8334(a), 8334(k), or 8422(a) of title 5, United States Code, as is applicable.