Pennsylvania is an employment at will state, so you can be terminated for any reason except for discrimination and also there are protections when exercising your rights to form a union. The information that you provided does clearly indicate that you were discriminated agaisnt or were fired for retailition for union activity. But, if the employer's actions were merely pretext because of your union activity then there may be rights that were violated. You are welcome to call my office to discuss this matter further. 412-788-7560.
If you are an at-will employee, you can be fired for any reason or no reason, except unlawful discrimination.
If you do not have an employment contract your recourse is limited. With the union on your side maybe there is help.
You might find my Legal Guide helpful "Workplace Discrimination: A Basis for Wrongful Termination Claims"
You might find my Legal Guide helpful "How to Choose A Lawyer For You"
You might find my Legal Guide helpful " What Do I Tell My Lawyer"
No one can know what the personel file record is in the matter because online we cannot find out any details. If you have a discrimination theory about hostile workplace conditions or that retaliation due to your union was the cause of your firing you'll need a lawyer. Check with a lawyer in your locale to discuss more of the details.
Good luck to you.
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