Some states have emploment at will laws but if you have a contract or something binding then it should be more difficult for them to let you go.
NLSA - Getting Fired
you can be fired for just about any reason (or no reason) at all. The normal rule in Pennsylvania (and some other states) is "employment-at-will". That means that most of us can be fired for just about any reason. Most of us can be fired because our boss doesn't like us, or because it is raining outside. However, if you have an employment contract, your employer may be able to fire you only for specific reasons. For instance, government employees and union employees can usually be fired only "for cause". If you have an employment contract, you must examine it closely to determine if it limits the reasons for which you can be fired.