You don't mention what state you are in, but the vast majority of states (with the exception of Montana) are "at will" employment states. At will is an employment arrangement in which the employee may quit at any time, and the employer may fire the employee for any reason that is not illegal. In the absence of an employment contract
or union agreement that grants you more rights, you are an at will employee (as the vast majority of employees are). Even if you are an at-will employee, you still cannot be fired for reasons that are illegal under state and federal law. In these situations, the government has decided to make an exception to the general rule of at-will employment.
For example, if your employer is subject to federal and state laws prohibiting job discrimination
(as all but the smallest employers are), you cannot be fired because of certain characteristics, such as your race, religion, or gender. Similarly, you cannot be fired because you have complained about illegal activity, about discrimination or harassment, or about health and safety
violations in the workplace. And you cannot be fired for exercising a variety of legal rights, including the right to take family and medical leave, to take leave to serve in the military, or to take time off work to vote or serve on a jury.So, even if the employer took the side of the superior over you, that's not unlawful, unfortunately. However, if anything was said that wasn't truthful, that could be considered defamation of character and you may have possible cause of action for that.