Employment law varies state to state, so to really discuss this intelligently, one would have to know which state this occurred in.
If you are in an At-Will employment state, an employer can discharge you because they don't like the car you drive. It may seem unfair, but it's a fact.
What it sounds like from what you have said is that you were outspoken and they viewed this as a threat. Nobody may have agreed with the new policy but you were the one who stood up and said so. It happens.
My belief on this is - better to find a new job and go where the atmosphere is more conducive to what you are looking for. As you said, they were instituting policy that you did not agree with. So, why stay? Move on and don't look back!