In August 1906, six months after his first official warning on the incompatibility of the new French Law of Separation with Catholic doctrine (see our previous posts on Vehementer Nos here and here), and after reviewing all legal and canonical possibilities, the Holy Father had no option but to proclaim, in the Encyclical Letter Gravissimo Officii Munere, that the nature of the religious associations (Associations Cultuelles) created by the Law was unacceptable to the Catholic Church. Pope St.Pius X offered a true lesson on the limits of the authority of temporal powers on the liberty of the Church:
Therefore, after having condemned, as was Our duty, this iniquitous law, We have examined with greatest care whether the articles of the said law would leave Us any means of organizing religious life in France in such a way as to safeguard from injury the sacred principles on which Holy Church reposes. ... And now, knowing your views as well as those of several cardinals, and after having maturely reflected and implored by the most fervent prayers the Father of Lights, We see that We ought to confirm fully by Our Apostolic authority the almost unanimous decision of your assembly.
It is for this reason that, with reference to the associations for public worship as the law establishes them, we decree that it is absolutely impossible for them to be formed without a violation of the sacred rights pertaining to the very life of the Church.
... while the law remains what it is, We declare that it is not permissible to try this other kind of association as long as it is not established in a sure and legal manner that the Divine constitution of the Church, the immutable rights of the Roman Pontiff and of the Bishops, as well as their authority over the necessary property of the Church and particularly over the sacred edifices.
With reference to the special charge against the Church of having been more accommodating in a similar case outside France, you should explain that the Church has acted in this way because the situations were quite different, and above all because the Divine attributes of the hierarchy were, in a certain measure, safeguarded. If any State has separated from the Church, while leaving to her the resource of the liberty common to all and the free disposal of her property, that State has without doubt, and on more than one ground, acted unjustly; but nevertheless, it could not be said that it has created for the Church a situation absolutely intolerable. But it is quite otherwise today in France; there the makers of this unjust law wished to make it a law, not of separation, but of oppression.
The legal standing of the Church in France would only be settled with a change in the interpretation of the Law of Separation, which allowed for a common understanding, between the Holy See and the French Republic, of the so-called "Diocesan Associations", accepted by Pius XI in 1924 (Maximam Gravissimamque).