Can I be forced out of my position if it’s not based on job performance?

I work for a local grocery store chain in Maryland. I have been in the position of Assistant General Manager for about 2 years. When I was offered the position, I was not given any job description, job requirements/expectations, and I did not sign anything. My employer has said that I am good at my job and I have been extremely reliable. Because of this, they wanted me to transfer to another store to help out. I refused because it is a farther drive and I’m not getting any pay increase. They told me if I don’t transfer I have to step down from my position. I told them I never agreed to transfer stores and it was never stated it was a requirement of my position. They said I should have signed something but when I told them I was never presented with anything to sign they just said transferring was “the nature of the business” and a “job expectation”. I am being forced to step down from my position for this sole reason, it has nothing to do with job performance. Is this legal?