Would not such apparent preference of Catholic employees justify Protestants in boycotting Catholic labor?
No. No evil has been done. And even had it been done, you are not justified in rendering evil for evil. 1033. Is it a sin for a Catholic to employ a Mason? No. The Freemason may have no personal antipathy towards Catholics at all, and even if he had, the law is, “Do good to those who hate you.” If a competent Catholic applies for a position together with a Mason, a Catholic may employ his fellow Catholic by preference because he wants to do a good turn to a fellow Catholic from a motive of fraternal charity. But he must not consider as a reason for this the doing of a bad turn to the Mason. That would be quite un-Christian and un-Catholic. 1034. If a Catholic employs a Mason, what should other Catholics do? They should behave just as they would otherwise. If a Catholic did do a bad thing by employing a Mason, who are his fellow Catholics to judge him and inflict a penalty? They must leave that to God. But, as I have said, a Catholic does not do any evil by employing a Mason. In purely
