Pope John XXIII
Mater et Magistra §139
Mater et Magistra: On Christianity and Social Progress
139 Hence, in Quadragesimo Anno Pope Pius XI rightly observed that "a proper proportion between different wages is also a matter of importance." He continued: "And intimately connected with this is a proper proportion between the prices charged for the products of the various economic groups, agricultural, industrial, and so forth." (39)
Source: Mater et Magistra (Vatican.va)