What you have described sounds hostile, but may not create a claim unless it is related to a protected category like race, sex, disability, age, etc... If the conduct is related to discrimination, contact a local employment attorney. Also, as a union member, you may have protections from this type of conduct. Good luck.
I don't see anything actionable in your post. It's not bullying or harassment or hostile work environment under the law. She does not like you, and has every right to be cold, and tattle. It is also not against the law to be in a clique, exclude others, be unforgiving, and be mean.
The only unlawful discrimination (where treating you differently can be actionable) is that which is based on race, religion, ethnicity, gender, age, disability, sexual orientation and familial status. Even then, it is a high burden to prove with evidence, a court will not entertain hunches, hearsay, conjecture or speculation.
Other than the above categories, the employer is allowed to treat people differently and discriminate on any other basis. What you describe is a bad place to work with petty and mean co-workers, most likely an inept supervisor also--it's not illegal.
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