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.

Radio Replies Volume 1 by Rev. Dr. Leslie Rumble MSC and Rev. Charles Mortimer Carty