uh, you just can.

theres no chances involved here.

you said union amd he imediately switched from negotiating a raise to firing you

all kidding aside, you don’t have a case here that I can see. if I were your boss I’d simply say “I asked him for a number and he gave me an answer that wasn’t a number so I stopped negotiating.” that would hold up fine. and then I’d probably go cry myself to sleep about being a corporate shit. Also, he was clearly already in the process of firing you (or accepting your constructive resignation) when you brought up the union. I say this only because I don’t want you to waste time, energy, or money on something a judge will throw right out of court.