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I'm sorry to hear about your situation. First of all, you need to understand that Minnesota is an "at will" employment state. At-will employment means that without a contract, you have no contractual or other right to employment with the company. The company is entitled to fire you for any reason: a good reason, a poor reason, or no reason at all--as long as the company does not fire you for an illegal reason (race, gender, age, religion, etc...). But it extends beyond firing, to hiring, promotions, demotions, wage cuts and raises, disciplinary actions, and even scheduling. Unless you can show that this was done in violation of a contract, union agreement, or a clear violation of an unambiguous and binding clause against the employer, or that it was done because of some minority status (age, race, gender, religion, disability) that you have, then they do have this discretion.
Now a union collective bargaining agreement is a contract, but you have to show specifically how they violated the contract. Typically such a contract deals with specifics (days off, pay, benefits, etc...) rather than interpersonal issues, although it's possible that yours could still govern your situation. It's not likely, mind you, but it's possible. If the contract is silent as to the situation, "at will" employment would then control.
As for "hostile work environment", this does not qualify. That is actually a legal term of art that only applies in sexual and race harassment cases.That is, if a workplace was "highly sexualized" (porn on the computers, dirty jokes all the time, etc...) that could qualify as a "hostile work environment". But again, that's a legal term of art, and the ordinary definition of what would be "hostile" does not mean the same there.
I know this is probably not what you wanted to hear, but it is the law. I hope that clears things up anyway. If you have any other questions, please let me know. If not, and you have not yet, please rate my answer AND press the "submit" button, if applicable. Please note that I don't get any credit for the time and effort that I spent on this answer unless and until you rate it positively (good or better). Thank you, ***** ***** luck to you!