2 We recall, but with sorrow, those sad days when in your country the evil project of separating the interests of the Republic from those of the Church was conceived and how, what is more unfortunate, steps were taken to put the project into execution. We cannot forget either how, at one fell stroke, the relations which existed between the Holy See and France were brusquely and unjustly broken off, how on December 9, 1905, the law of separation was passed by which the Concordat which had been in force over a long period of time was abrogated by but one party to the contract in direct violation of all the formalities demanded by law, how also, without the slightest regard either for the hierarchy of the Church or for the authority of the Holy See, unjust and arbitrary laws were enacted concerning the rights and possessions of the Church, as well as on the subject of divine worship. Neither can We forget how Our Predecessor of saintly memory, Pius X, in his encyclical Vehementer of February 11, 1906, and in the allocution which he made at the Consistory of February 21, the same year, condemned in no uncertain terms and with all possible solemnity this very law; nor how he condemned, at the same time, the so called "Associations Cultuelles" which were to be established in the spirit of that law, Associations which in another encyclical Gravissimo of August 10, of that year, the same Pope rejected once more and condemned.
Source: Maximam Gravissimamque (Vatican.va)