The Uniformed Services Employment and Reemployment Rights Act (USERRA) of 1994 is a federal law intended to ensure that persons who serve in "uniformed services" (1) are not disadvantaged in their civilian careers, (2) are promptly reemployed in their civilian jobs, and (3) are not discriminated against in employment.
Essentially, the Act requires employers to allow those who have served on active duty to go back to the same job and at the same pay after they return from such active duty service. The Act does, however, contain two important exceptions for employers under which employers are not required to reemploy a service man or woman, specifically when (1) the employer experiences "changed circumstances" (e.g., during a company-wide layoff) and (2) when there is "undue hardship" (e.g., the employer is facing severe financial difficulties).