ON THE "ECUMENICAL MOVEMENT"
An Instruction of the Holy Office
Addressed to the ordinaries of places, given December 20, 1949. V
—Although in all these meetings and conferences any communication whatsoever in worship must be avoided, yet the recitation in common of the Lord's Prayer or of some prayer approved by the Catholic Church, is not forbidden for opening or closing the said meetings.http://www.ewtn.com/library/CURIA/CDFECUM.HTM