220.127.116.11 Catholics as Witnesses at Baptism in an Ecclesial Community
1. Although Catholics may serve as witnesses at baptism conferred by an ecclesial community, they are to be advised to decline this role when the person presented for baptism has already received valid baptism, or is the child of Catholic parents who is handed over to a non-Catholic religion, or when a valid Christian baptism would not be administered. 
 CC. 1366 and 845 §1, Ecumenical Directory, n. 98.