Employment at Will
Courts have ruled that because the person was an at-will employee and was not covered by contract (such as a union contract), the "employer may terminate an employee at any time or any reason for no reason".
Most Americans don't realize that unless you work for the government or belong to a union, under the laws of nearly all the states you are considered an "at-will-employee" and it is perfectly legal for your employer to fire you for no reason at all!