Can my owner legally demote me?

Okay, so I’ve been with Jimmy johns since June of 2024. I started as a driver, and worked my way up to 1st Assistant manager. Due to the difficult nature of our owners, my GM stepped down. The owner is now trying to give my current spot to the previous GM, and demote me while also decreasing my pay. Just for some background, I have stayed through several walk outs. I was promised a raise after completing my fasttrack, and when the time came, the owner refused to give it to me. I had to essentially threaten to quit. We are only just now properly staffed after 5 month of me and my GM essentially working on call. Today he took me to the back and tried to get me to sign a paper agreeing to a demotion and pay decrease. I asked him if he’d rather find someone to fill my position than pay me my current wage, and he said “Yes. Does that mean you’re putting in your two weeks?” So as of right now my two weeks has been put in verbally. I have one write up, and it’s from when I was a driver. I’ve done nothing wrong, and the owner even admitted that I was not at fault. He is always trying to pull a fast one on his employees, and has had several GM’s and AM’s walk out on him. Is he even legally allowed to demote me without some type of disciplinary actions?