71 Pa. C.S. § 5953.3
Notwithstanding any other provisions of this part, a domestic relations order pertaining to a member may provide for an irrevocable survivor annuitant. A domestic relations order requiring the designation of an irrevocable survivor annuitant shall be deemed to be one that requires a member to designate an alternate payee as a survivor annuitant and that prohibits the removal or change of that survivor annuitant without approval of a court of competent jurisdiction, except by operation of law. Such a domestic relations order may be certified as an approved domestic relations order by the secretary of the board, or his designated representative, in which case the irrevocable survivor annuitant so ordered by the court cannot be changed by the member without approval by the court. A person ineligible to be designated as a survivor annuitant may not be designated as an irrevocable survivor annuitant.
71 Pa.C.S. § 5953.3