Pope Paul VI
Sacerdotalis Caelibatus §8
Sacerdotalis Caelibatus: On the Celibacy of the Priest
8 It is asserted, moreover, that the maintaining of priestly celibacy in the Church does great harm in those regions where the shortage of the clergy—a fact recognized with sadness and deplored by the same Council (4)—gives rise to critical situations: that it prevents the full realization of the divine plan of salvation and at times jeopardizes the very possibility of the initial proclamation of the Gospel. Thus the disquieting decline in the ranks of the clergy is attributed by some to the heavy burden of the obligation of celibacy.
Source: Sacerdotalis Caelibatus (Vatican.va)