Unfortunately, if you did not have an employment contract protecting your employment, by limiting the reasons for which you could be fired, guarantying employment for some term, or providing a process which must be fired for discipline or termination, you probably cannot make a wrongful termination claim. That is because without a contract, you would be an employee at will, and an employee at will may be fired at any time, for any reason--and that includes that a new GM does not approve of a policy or practice which a prior GM had allowed. You are not guaranteed any warning or notice or chance to change what you're doing if you are an employee at will, and the employer can terminate you immediately.