There are certain reasons that you can never use to fire an employee.

Most employees in the United States work "at will." This means that they can quit at any time, for any reason, and that you can fire them at any time, for any reason -- unless that reason is illegal. State and federal laws prohibit employers from relying on certain justifications for firing employees, set out below. These prohibitions apply whether the employee has an employment contract with you or works at will.

Discrimination

Federal law makes it illegal for most employers to fire an employee because of the employee's race, gender, national origin, disability, religion, or age (if the person is older than 40). Federal law also prohibits most employers from firing someone because that person is pregnant, has recently given birth, or has a related medical condition.

Most states also have anti-discrimination laws that prohibit firing for all of the reasons listed in the federal law. Many state laws, however, are broader than federal law, meaning they include additional prohibitions (for example, some state laws prohibit discrimination on the basis of sexual orientation or marital status), and they cover a wider range of employers. To learn more about your state anti-discrimination laws, contact your state fair employment office.