16 It is well to observe that to approve such an iniquitous law, or spontaneously to give to it true and proper cooperation, is undoubtedly illicit and sacrilegious. but absolutely different is the case of one who yields to such unjust regulations solely against his will and under protest, and who besides does everything he can to lessen the disastrous effects of the pernicious law. In fact, the priest finds himself compelled to ask for that permission without which it would be impossible for him to exercise his sacred ministry for the good of souls; it is an imposition to which he is forced to submit in order to avoid a greater evil. His behaviour, consequently, is not very different from that of one who having been robbed of his belongings is obliged to ask his unjust despoiler for at least the use of them.
Source: Acerba Animi (Vatican.va)