Department not giving me TAships after a dispute with professor, what should I do?
The first thing would be to meet with the department chair to get the story. If that doesn't yield a satisfactory result, many universities have an appeals process, and you could call on that avenue. If teaching is an actual requirement, then they would need a pretty compelling reason to effectively terminate you without just cause and doing the Due Process thing, although this depends on the legal system in your country, of course. But you would have to be pretty blameless (e.g., if the dispute was over a significant error on your part as a teacher, that could be the end of the discussion).