Employer Demoting Me After Mental Health Crisis

Hi. I’m looking for advice on my rights in this situation. I’m in Michigan. I have worked for an employer for 7 years. Back in August of this year, I took an 8 week leave of absence for mental health issues and returned in October. Since then, I have been written up twice for being late a few minutes (I’m talking less than 5) because I didn’t immediately let upper management know I was running behind. Yesterday, at 3:30pm, I was called into a meeting with my direct supervisor and HR and was told that I’m being demoted and it’s a 30k a year pay cut. If I choose not to take the demotion, I am done working effective immediately Monday morning. They said I could keep my seniority and that they aren’t ruling out a repromotion in the future when I’ve “recovered”. Is this legal? I did not have intermittent FMLA or any ADA accommodations for this position.