9 Education has been declared free, but with these important restrictions: both priests and religious are forbidden to open or to conduct elementary schools. It is not permitted to teach children their religion even in a private school. Diplomas or degrees conferred by private schools under control of the Church possess no legal value and are not recognized by the state. Certainly, Venerable Brothers, the men who originated, approved, and gave their sanction to such a law either are totally ignorant of what rights pertain jure divino to the Church as a perfect society, established as the ordinary means of salvation for mankind by Jesus Christ, Our Redeemer and King, to which He gave the full liberty of fulfilling her mission on earth (such ignorance seems incredible today after twenty centuries of Christianity and especially in a Catholic nation and among men who have been baptized, unless in their pride and foolishness they believe themselves able to undermine and destroy the "House of the Lord which has been solidly constructed and strongly built on the living rock") or they have been motivated by an insane hatred to attempt anything within their power in order to harm the Church. How was it possible for the Archbishops and Bishops of Mexico to remain silent in the face of such odious laws?
Source: Iniquis Afflictisque (Vatican.va)