50 USC 2021 - Contributions to fund

(a) In general 

(1) Participant’s contributions 
Except as provided in subsection (d) of this section, 7 percent of the basic pay received by a participant for any pay period shall be deducted and withheld from the pay of that participant and contributed to the fund.
(2) Agency contributions 
An equal amount shall be contributed to the fund for that pay period from the appropriation or fund which is used for payment of the participants basic pay.
(3) Deposits to the fund 
The amounts deducted and withheld from basic pay, together with the amounts so contributed from the appropriation or fund, shall be deposited by the Director to the credit of the fund.

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(b) Consent of participant to deductions from pay 
Each participant shall be deemed to consent and agree to such deductions from basic pay, and payment less such deductions shall be a full and complete discharge and acquittance of all claims and demands whatsoever for all regular services during the period covered by such payment, except the right to the benefits to which the participant is entitled under this subchapter, notwithstanding any law, rule, or regulation affecting the individuals pay.
(c) Treatment of contributions after 35 years of service 

(1) Accrual of interest 
Amounts deducted and withheld from the basic pay of a participant under this section for pay periods after the first day of the first pay period beginning after the day on which the participant completes 35 years of creditable service computed under sections 2081 and 2082 of this title (excluding service credit for unused sick leave under section 2031 (a)(2) of this title) shall accrue interest. Such interest shall accrue at the rate of 3 percent a year through December 31, 1984, and thereafter at the rate computed under section 8334 (e) of title 5, and shall be compounded annually from the date on which the amount is so deducted and withheld until the date of the participants retirement or death.
(2) Use of amounts withheld after 35 years of service 

(A) Use for deposits due under section 2082 (b) 
Amounts described in paragraph (1), including interest accrued on such amounts, shall be applied upon the participants retirement or death toward any deposit due under section 2082 (b) of this title.
(B) Lump-sum payment 
Any balance of such amounts not so required for such a deposit shall be refunded to the participant in a lump sum after the participants separation (or, in the event of a death in service, to a beneficiary in order of precedence specified in subsection[1] 2071(c) of this title), subject to prior notification of a current spouse, if any, unless the participant establishes to the satisfaction of the Director, in accordance with regulations which the Director may prescribe, that the participant does not know, and has taken all reasonable steps to determine, the whereabouts of the current spouse.
(C) Purchases of additional elective benefits 
In lieu of such a lump-sum payment, the participant may use such amounts
(i) to purchase an additional annuity in accordance with section 2121 of this title; or
(ii) provide any additional survivor benefit for a current or former spouse or spouses.
(d) Offset for social security taxes 

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(1) Persons covered 
In the case of a participant who was a participant subject to this subchapter before January 1, 1984, and whose service
(A) is employment for the purposes of title II of the Social Security Act [42 U.S.C. 401 et seq.] and chapter 21 of title 26, and
(B) is not creditable service for any purpose under subchapter III of this chapter or chapter 84 of title 5,

there shall be deducted and withheld from the basic pay of the participant under this section during any pay period only the amount computed under paragraph (2).

(2) Reduction in contribution 
The amount deducted and withheld from the basic pay of a participant during any pay period pursuant to paragraph (1) shall be the excess of
(A) the amount determined by multiplying the percent applicable to the participant under subsection (a) of this section by the basic pay payable to the participant for that pay period, over
(B) the amount of the taxes deducted and withheld from such basic pay under section 3101 (a) of title 26 (relating to old-age, survivors, and disability insurance) for that pay period.
[1] So in original. Probably should be “section”.