Employment Law Questions? Ask an Employment Lawyer.
You have to first file a union grievance so that you can have all administrative remedies attempt first. This is a requirement before you take any other action....well, not a requirement, but it makes the case so much stronger that you really shouldn't do anything before completing the union grievance process.
Once that is completed, if there is no satisfaction, you have only one choice. You have to hire a local attorney to sue in state court for breach of contract. Your collective bargaining agreement is a contract with you (and everyone else) and you can sue individually for a breach of that agreement.