The TWU had some nasty provisions about that and were ruthless in pursuing them
The AFAP in the old days were not beyond the bully boy approach. The majority of our pilots were members and a couple of our boys did all the donkey work in negotiating award details with the company. AFAP were a rubber stamp basically, besides being the agent to whom the judge talked to formalise arrangements. A disagreement came about (forget what) and our reps were told (threatened??) that they, the AFAP, would get Norm Gallagher (remember him?) and his muscle to pay a visit and show us the error of our ways. The result was all AFAP members bailed and we set up our own union.