Can I sue my employer for demoting me without notice?

I worked at my job for 3 years now. Right now it turns out that my boss had me demoted without any notice and hasn't been telling me that I was not doing something right. I had only one bad incident 5 months before hand when I under-cooked fish, and I have not gotten a complaint sense, not even a right up. I have been getting better and I even ask people personally if they like it or not. Don't I have a right to be aware of any problems or errors before the processes of being demoted?