I’ve seen several posts of people asking for advice on situations like this with so many answers suggesting OP to fight back, document and contact the union, but this seems too much work for an unconvincing result, because there is no way a manager is going to fire an employee or a clique for a “he claims she claims” situation.

Manager, employer, even the union, will listen to you, play theatrics and change nothing hoping you forget.

Walking away, while making you feel like a loser, seems to be the sane choice long term. Cliques are gonna clique.

Maybe you can think of a better way?