Under the federal Employee Polygraph Protection Act of 1988(29 USC 2001et seq.), most private employers are prohibited from requiring employees or prospective employees to submit to lie detector tests. The law defines a "lie detector" as any mechanical or electrical device that is used to render a diagnostic opinion about the honesty or dishonesty of an individual. The definition includes polygraphs, deceptographs, voice stress analyzers, psychological stress evaluators, and similar devices (29 USC 2001). It is also illegal to use or inquire about a lie detector test conducted by someone else (29 USC 2002).
Subject to certain restrictions, any employer may legally request that an employee take a lie detector test as part of an ongoing investigation involving economic loss or injury to the employer's business, such as theft, embezzlement, misappropriation, or industrial espionage or sabotage. However, such tests can be administered only to employees who are reasonably suspected of involvement, and they must have had access to the property that is the subject of the investigation to justify testing.