回复：老板突然翻脸，敬请帮助指教！急急急！！！

Your boss can not fire you if you have offer letter signed by the Director or Chairman of your department. I know some school like Baylor College of Medicine have Employment Relations at HR. Check the HR of your school for the policy regarding this. They have right to force them to complete the contract if there is a policy in your school. Usually,schools follow the law of the state that you live at present.