Here is the problem. Hostile work environment is a very specific claim, defined by the U.S. Supreme Court.
That Court stated that hostile work environment only involves harassment that is based on race, religion, gender, age, disability or FMLA use. The Court also noted that our employment laws
are not a civility code. Harassment, poor work conditions
, generally bad bosses, these things are not covered.
Some states have seen a problem with that and have tried to pass workplace dignity laws that would apply in this sort of situation, but no state has managed to pass such a law yet.
What that means, unfortunately, is that this sort of petty office politics is not illegal. Unless you have some sort of contractual guarantee to remain on a certain shift, the employer legally can change that shift at any time, with or without your consent unless it is for one of the illegal reasons that I've outlined and a few others.
The list is not large. Race, religion, gender, age, disability, FMLA use, worker's compensation retaliation
complaint retaliation, Department of Labor
complaint retaliation, Sarbanes-Oxley retaliation (for securities and banking jobs).
If you can't fit this harassment into one of those categories, there just isn't any law against it. I wish I could tell you differently here, but that is the state of the law in this situation. I sue employers for a living and I promise you, if there was something I could tell you to get this resolved in your favor, I would. I'm simply respecting you enough to be honest with you here.