So many here have been victimized by job or pay changes, but there is a fix:
When hired, get everything you can in writing. Hours, location, pay, benefits, schedule requirements, separation procedure…..
You know what you would have if you got it? A contract. It's what unions do, and they work.
Is there an employee manual? Read every line. The union will do it with you.
Just having a contract backed by a union is worth the dues. It's why your bosses hate them so.