Federal Law Federal law requires employers to hire only individuals who may legally work in the United States—either U.S. citizens or foreign citizens who have the necessary authorization. To comply with the law, employers must verify the identity and employment authorization of each employee hired to work in the United States by completing and retaining Form I-9. E-Verify is an Internet-based system that allows an employer, using information reported on an employee's Form I-9, to determine the eligibility of that employee to work in the United States. Use of E-Verify is mandatory for certain federal contractors. Some private companies may also be required by state law to use E-Verify.