Seems BALPA are having a bad week. Another mis-step from them joining with UNITE to try to stop non-union members from receiving holiday pay. It's either a right or it's not, if it's not a right then hand back the money you won, don't try to keep it from others.
The concept should be familiar to the unions, things like equal pay for women - just because the union led the fight, should only union members get equal pay.
This is petty and beyond contempt.