54 Associations of every kind, and especially those of working men, are now far more common than heretofore. As regards many of these there is no need at present to inquire whence they spring, what are their objects, or what the means they imply. Now, there is a good deal of evidence in favor of the opinion that many of these societies are in the hands of secret leaders, and are managed on principles ill - according with Christianity and the public well-being; and that they do their utmost to get within their grasp the whole field of labor, and force working men either to join them or to starve. Under these circumstances Christian working men must do one of two things: either join associations in which their religion will be exposed to peril, or form associations among themselves and unite their forces so as to shake off courageously the yoke of so unrighteous and intolerable an oppression. No one who does not wish to expose man's chief good to extreme risk will for a moment hesitate to say that the second alternative should by all means be adopted.
Source: Rerum Novarum (Vatican.va)