How do you answer 'Why did you leave your last company' in a job interview?

If you tell the truth......will you be hired? I was actually looking to find an answer here!

This has been haunting me for 2 1/2 years now and I am about to interview for a job that I want so bad I could taste it....and I know for a fact that this employer checks with previous employers.....thus....giving me no choice but telling the truth. I was fired for attempting to get a union in.

REASON FOR LEAVING: Irreconsilable differences

Myself and several co-workers tried to form a union.....when the Receiving Manager....a former disgruntled boyfriend of mine learned of this......he went to the Plant Manager....informed him of the union and named a few of us involved. I confronted the ex-boyfriend.....Words got a little heated with his buddy as a witness....I was fired the next working day for conduct not being of company standards. Two weeks later another was fired......two weeks after that another....then another.....etc. Because we didn't have enough signed union cards in our possession at the time...the union refused to help us get our jobs back.

Of course....my prospective employer is a union shop!