It is illegal for an employer to retaliate against an employee who complains about possible disrimination or harassment at work.  It is also illegal for an employer to retaliate against an employee who assists another employee in making a complaint about discrimination or harassment.   The purpose of this law is to protect employees who complain about employment discrimination or harassment and to protect other employees who may serve as witnesses to the discrimination or harassment.  

The U.S. Supreme Court strictly upholds this law as it essential for the employment discrimination laws to carry out their purpose.   Retaliation is broadly defined to include virtually any kind of negative action by the employer.  Retaliation can even include the assignment of undesirable job duties, even if those duties are within the employee's job description.   Therefore if an employee complains about employment discriminatin or harassment, the employer is prohibited from taking any action of any kind against the employee.