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5 U.S. Code § 8417 - Survivor reduction for a former spouse

If an employee or Member has a former spouse who is entitled to a survivor annuity as provided in section 8445, the reduction described in section 8419(a) shall be made.
An employee or Member who has a former spouse may elect, under procedures prescribed by the Office, a reduction in the annuity of the employee or Member under section 8419(a) in order to provide a survivor annuity for such former spouse under section 8445.
An election under this subsection shall be made at the time of retirement or, if the marriage is dissolved after the date of retirement, within 2 years after the date on which the marriage of the former spouse to the employee or Member is so dissolved.
(3) An election under this subsection—
(A) shall not be effective to the extent that it—
(i) conflicts with—
any court order or decree referred to in section 8445(a) which was issued before the date of such election; or
any agreement referred to in such section 8445(a) which was entered into before such date; or
would cause the total of survivor annuities payable under sections 8442 and 8445, respectively, based on the service of the employee or Member to exceed the amount which would be payable to a widow or widower of such employee or Member under such section 8442 (determined without regard to any reduction to provide for an annuity under such section 8445); and
shall not be effective, in the case of an employee or Member who is then married, unless it is made with the spouse’s written consent.
The Office shall by regulation provide that subparagraph (B) may be waived for either of the reasons set forth in section 8416(a)(2).