If someone wants to get rid of an employee for one reason that is illegal, they just make up another excuse or they put them in a near useless position with no chance of being promoted in hopes they quit. I've seen this occur multiple times and had it happen to me a few years ago when I wouldn't participate in my boss's Limbaughesque political rants. Most of the times it's not even worth going to court over as you would be better off spending that time looking for a better job and are unlikely to win anyways unless you have strong evidence.