There used to be tenure. After I had been teaching a few years, I was called to my principal's office to sign my "tenure papers." Basically, I think tenure gave me the right to due process if I were disciplined. Prior to having tenure, my right may have been more limited.
Mja is correct, teachers get fired all the time. If you read the minutes of each SRC meeting there are lists of terminations. No reasons are given but there they are.