I am not an attorney but have done a lot of legal work in various companies I have been involved with and have a lot of experience with employment contracts. You definitely need an attorney that specializes in employment law and I might be able to recommend several but I would some additional info about your situation. Your profile doesn't list an email or phone so if you want to provide a way to contact you I can get in touch to see if I can help further.
If you don't know any attorneys at all then just google some local ones and call 'em up. If they can't help you they will refer you to a buddy that can. Otherwise call an attorney you happen to know or know of for same. Pretty much all of them should be competent enough to write a letter for you and get the ball rolling.
They refer to themselves as "Employment Lawyers." Don't know where you are, but googling "Employment Lawyer NYC" gives me back a gajillion results. If you're in NYC, I can give you a recommendation (my email address is in my profile)