Most employees in the US work "at will", which means that they can be dismissed (or fired) by an employer for any reason and at any time. They cannot, however, be fired for illegal reasons, which includes discrimination and retaliation. Even if an employee has an employment contract with his or her employer, however, he or she cannot be fired for illegal reasons. An employee cannot be fired because of race, gender, national origin, disability, religion, or age. It is illegal for an employer to fire someone because she is pregnant or has a medical condition related to pregnancy or childbirth. It is illegal for an employee to be fired for asserting his or her rights and filed a claim against the employer. The federal government prohibits an employee being fired for refusing to take a polygraph (or a lie detector) test. Most states prohibit an employer from firing someone in "violation of public policy", meaning for reasons society finds morally or ethically wrong.