I used to work for my brothers IT company. His partner tried to buttfuck me over something and gave me the weekend to think it over.... if i didnt agree to his wishes it was made clear that there would be no place for me at work. I said i want to start the greivance procedure to my brother, who advised me it wouldnt be in my best interests, which i took as a clear threat. I ended up finding a new job and left anyway. I was spoken to 'off the record' and was told if i continued with the procedure and it went to tribunal he would just lie and make me out to be the bad egg.
I now work for a much larger company, and im sure if i wanted to do the same here, it would be taken seriously. But working for a small company, it wasnt worth a shit!
HTH