The salary of an employee can be reduced if the employee's employment is considered hired at will. This type of employee does not have a formal employment contract with terms regarding reduction of salary or wages. Employees under individual or union contracts are usually protected against salary or wage reductions.
An employer cannot reduce the salary of an employee due to discrimination. This includes race, sex or age of the employee. Employees are also protected if they need to attend jury duty or to serve in the National Guard.
If the salary of an employee is reduced, it cannot be brought down past the minimum wage regulations enforced at the state level by the Department of Labor.