What is the statute of limitations when you are relieved of a job so that someone else can be hired?

I have been working for my township for 5 years. A little over 4 years in one office and 9 months in another. I was switched due to the fact that the Mayor of my town promised his sister-in-law my position. I was unjustly blamed for things that were either ridiculous or false. I was told that my boss kept a binder of my mistakes but was not allowed to view it. Instead of letting me go altogether I was switched to another department after I explained to our Township manager that all of my bosses issues with me started right after I told her I was diagnosed with Parkinson's. This occurred 9 months ago and I have been working in this new department since. I have been since made aware that the Mayor's sister-in-law is making about $6 more an hour than I did and that her title was changed so she did not have to pay Union dues as I did. I am in the Teamsters Union, and they did nothing to help me during this time. So I have a case and do I have time to sue if I decide to?