The Church has long taught that defrauding a worker of his wages is one of the four sins that cry out to heaven for vengeance (CCC 1867). In his landmark encyclical Rerum Novarum, Pope Leo XIII echoed the words of St. James:OK, so that's a lot of backstory. We know the Church believes this. So what?
Doubtless, before deciding whether wages are fair, many things have to be considered; but wealthy owners and all masters of labor should be mindful of this – that to exercise pressure upon the indigent and the destitute for the sake of gain, and to gather one’s profit out of the need of another, is condemned by all laws, human and divine. To defraud any one of wages that are his due is a great crime which cries to the avenging anger of Heaven. “Behold, the hire of the laborers… which by fraud has been kept back by you, crieth; and the cry of them hath entered into the ears of the Lord of Sabaoth.” Lastly, the rich must religiously refrain from cutting down the workmen’s earnings, whether by force, by fraud, or by usurious dealing; and with all the greater reason because the laboring man is, as a rule, weak and unprotected, and because his slender means should in proportion to their scantiness be accounted sacred. Were these precepts carefully obeyed and followed out, would they not be sufficient of themselves to keep under all strife and all its causes?
Again, Pope Pius XI took up the cause in Quadragesimo Anno. He made an important distinction, however, when it came to those businesses which themselves were deprived of enough revenue to pay their workers justly:
[I]f the business in question is not making enough money to pay the workers an equitable wage because it is being crushed by unjust burdens or forced to sell its product at less than a just price, those who are thus the cause of the injury are guilty of grave wrong, for they deprive workers of their just wage and force them under the pinch of necessity to accept a wage less than fair.
First, there is the problem of working for the Church herself. There is no surer path to financial insolvency than for a hard worker to direct their energies towards some form of full-time Catholic apostolate, or to slave away for long hours as a Director of Religious Education, or to teach at a Catholic school.... This becomes a particular problem if they embody the Catholic ethos of “oppenness to life” and have a large family.Emphasis added. This is a good point. Some religious orders require a vow of poverty, but a large part of the work is done by people who do not labor under such vows. How much stronger the moral argument would be if it were joined to practical example.
I suspect few individuals have ever had aspirations of becoming wealthy while working for the Church, but by the Church’s own teaching, the worker in a Catholic apostolate or school should expect to “be paid a wage sufficient to support him and his family.” (QA 71) It is inexcusably hypocritical that the same clergy who wield the Church’s social teaching as a weapon against the titans of industry — often claiming that this is a non-negotiable moral imperative — often fail so completely when it comes to applying this standard to those under their own employ.