It is true that due to the nature of at-will employment in the United States, employers have a lot of discretion when it comes to both hiring and firing. This means that wrongful termination can be very hard to prove in many instances.
However, even though the majority of US employment is at-will, this does not mean that wrongful termination never occurs. According to Findlaw, firing an employee for discriminatory reasons, retaliatory reasons, or whistleblowing is not allowed under at-will employment.
What is a discriminatory reason to fire an employee?
This is probably the most common form of wrongful termination. If you are a member of a protected group and your employer fires you for this association as opposed to performance-related problems, then it is likely this is wrongful termination.
There are some groups that federal law protects, such as gender, origin, race, religion, pregnancy, and age. In some localities, the law also protects sexual orientation and gender identity.
What is a retaliatory reason to fire an employee?
It is not legal for employers to fire employees as punishment in many instances. For instance, if an employee is suffering from discrimination and files a complaint with the EEOC, the employer may not terminate that employee in response. Employers may also not terminate employees for taking permitted medical leave or actively participating in violation investigations.
Employer may not fire employees who report health and safety violations or disregard for environmental law on the part of the employer. It is important for the employee to keep careful records if an employer terminates him or her for whistleblowing.