Contact an employment attorney ASAP. There are many facts that need to be explored, including the wording of your union contract, your length of employment, and the number of employees working for your employer. Depending on all the facts, there is the possibility of FMLA or disability claims, as well as the possibility that your union may have failed to represent you.
Answers to questions on this forum do not create an attorney-client relationship.
The answer is going to depend on many specifics you did not provide. Georgia law provides for a 6 year statute of limitation on most contract claims. Personal claims can be much shorter, sometimes one or two years. Claims based on discrimination have a 180 day window in which you must satisfy the administrative requirements (such as filing with the EEOC). In your case, there is the additional issue of your union contract, and whether the union represented your properly and in good faith. What your remedy may be is not clear from your description. You are going to need to talk to a good attorney who can listen to all your facts, look at your documentation, and offer you some specific advice that will fit your particular situation.
I am providing general information on the law only, and no attorney-client relationship exists by virtue of this exchange. You can not rely upon this as formal legal advice. If you require specific legal advice, you must hire an attorney and then your communications will be protected by attorney-client privilege, and you will have the benefit of an opinion of counsel. Call 770-753-9995 for a free evaluation.