That's a really strange sounding situation, you need to dig into it. It's possible to change unions. The Pilots at NetJets did it when they tossed out the Teamsters and voted in an in-house union.
I think (not certain) you need to have 50% +1 of the pilots sign cards for a new union election. You'll probably need a lawyer familiar with the process.

I suggest you (personally) tread lightly. As allude, you need more, better, or correct information, but just collecting it puts you in potential jeopardy. Ask yourself, are your workings conditions/compensation better or worse than if you flew for a comparable company? The risk is you lose your job and have to explain the reason in future interviews; not good. Too many have fallen on their sword in union related fights with non union companies. The pilots who will profit from those actions can never, and sadly, few feel the obligation to do so, thank or reward the instigator for the improvements they receive. Be safe