If you are a union member, then there is a contract between your employer and the union which likely contains the grounds, guidelines and procedures for the employer to be able to terminate an employee, the filing of a grievance, etc. You have to have your union represent you in that regard. Subject to the union contract, an employer wanting to terminate an employee for the reason you state is not, in and of itself, illegal and you provide no other facts which would indicate that the real reason for terminating you was an impermissible discrimatory ground.
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If the termination was due to your union activity, you may have a claim. You should contact your union and/or a labor law attorney.
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I'm not sure if you made a mistake by having parties in the building where you work. But if this is a Local 32BJ contract, supers are considered supervisors, even if they are in the union, and are held to a higher standard than porters and other union workers, meaning a super can be fired more easily.