Are you a unionized department? Can you go to your local representative? Can you go to your Health and safety rep (as a start) or perhaps your state rep.
What about your chain of command? It is possible that they are the problem, can you jump them (be prepared for the fall out, but it sounds like you're already experiencing a serious situation) and go to their bosses; such as the head of Emergency Services for the City, or someone like this. Human Resources, Labour Relations? I'm suggesting all of these options, as I'm not sure what you have available to you.
Best of luck and I hope all works out well for you.
Document, document, document. Write down such examples of harassment, favoritism, etc, what day it happened on, what was said, etc. Going in without documentation becomes a hearsay issue and can be difficult to prove. Contact those as already suggested, but if things are as serious as you indicate here, it is best to have your ducks in a row.
1. Keep you mouth shut.
2. Meet with an attorney.
3. Understand that there is not a lot you can do about this unless you have witnesses, and any kind of written documentation.
4. Quietly keep a log of everything that happens, everything. This is admissible in court.
5. Remain anonymous on the FFN to protect yourself.
6. Look at this site for some legal information and background. http://www.law.ucla.edu/volokh/harass/breadth.htm
7. Make the decision as to whether or not you really want to take this on. Sometimes it's a hell of a lot easier to just walk away... your call.