22 C.F.R. § 19.5-1
If a participant or former participant becomes divorced on or after February 15, 1981, he/she shall notify the Department (PER/ER/RET) of the divorce on or prior to its effective date. The notice shall include the effective date of the divorce, the full name, mailing address, and date of birth of the former spouse and the date of the member's marriage to that person, and enclose a certified copy of the divorce decree. If there is a court order or spousal agreement concerning payment or nonpayment of Foreign Service benefits to the former spouse, the original or a certified copy of the order or agreement shall also be forwarded to PER/ER/RET. In the absence of a court order or spousal agreement providing otherwise, the Department will pay a pro rata share of the member's benefits to the former spouse. (A former spouse of a former participant who separated from the Service on or before February 15, 1981 is not eligible for a pension under § 19.9 , i.e., not eligible for a pro rata share of the principal's annuity.) Upon receipt of notice of a divorce, a court order, or spousal agreement, the Department will proceed as indicated in § 19.6 or § 19.7 . Delinquent notice to the Department of the divorce of an annuitant will result in retroactive payments to any qualified former spouse to the extent that the retroactive payments can be deducted from future annuity payments to the principal as stated in § 19.6-4 .
22 C.F.R. §19.5-1