6 The extent of the injury inflicted on the Apostolic See by the unilateral abrogation of the Concordat is notably aggravated by the manner in which the State has effected this abrogation. It is a principle admitted without controversy, and universally observed by all nations, that the breaking of a treaty should be previously and regularly notified, in a clear and explicit manner, to the other contracting party by the one which intends to put an end to the treaty. Yet not only has no notification of this kind been made to the Holy See, but no indication whatever on the subject has been conveyed to it. Thus the French Government has not hesitated to treat the Apostolic See without ordinary respect and without the courtesy that is never omitted even in dealing with the smallest States. Its officials, representatives though they were of a Catholic nation, have heaped contempt on the dignity and power of the Sovereign Pontiff, the Supreme Head of the Church, whereas they should have shown more respect to this power than to any other political power - and a respect all the greater from the fact that the Holy See is concerned with the eternal welfare of souls, and that its mission extends everywhere.
Source: Vehementer Nos (Vatican.va)