There are repercussions! The union negotiates your contract and you follow it. Breaking the contract terminates your employment. Following your contract isn't lazy. Coworkers in private non-union industry hate the overachiever just as much. I promise.
I am in a private non-union industry and I celebrate my coworker overachievers because they usually get promoted and get a raise. Their achievements do not reflect that I am a poor worker.