53 Pa. Stat. § 881.120
Notwithstanding any other provision of this act, a domestic relations order may provide for an irrevocable beneficiary. A domestic relations order requiring the nomination of an irrevocable beneficiary shall be deemed to be one that requires a member to nominate an alternate payee as a beneficiary and that prohibits the removal or change of that beneficiary without approval of a court of competent jurisdiction, except by operation of law. A domestic relations order subject to this section may be certified as an approved domestic relations order by the secretary of the board or the secretary's designated representative after the member makes the nomination, in which case the irrevocable beneficiary ordered by the court may not be changed by the member without approval of the court.
53 P.S. § 881.120