15 Meanwhile, in order to remedy to some extent the calamitous conditions that afflict the Church in Mexico, We must avail ourselves of those means which We still have in hand, so that, by the maintenance of divine worship as far as possible in every place, the light of faith and the sacred fire of charity may not be extinguished among those unhappy populations. Certainly, the laws are iniquitous that are impious, as We have already said, and condemned by God for everything that they iniquitously and impiously derogate from the rights of God and of the Church in the government of souls. Nevertheless, it would be a vain and unfounded fear to think that one is cooperating with these iniquitous legislative ordinances which oppress him, were he to ask the Government which imposes these things for permission to carry out public worship, and hence to hold that it is one's duty to refrain absolutely from making such a request. Such an erroneous opinion and conduct might lead to a total suspension of public worship, and would, without doubt, inflict grievous harm on the entire flock of the faithful.
Source: Acerba Animi (Vatican.va)