The Immigration Reform and Control Act of 1986 requires employers to verify that employees are eligible to work in the United States, according to U.S. Citizenship and Immigration Services. This law prohibits employers from hiring unauthorized workers. The government created form I-9 to facilitate employee verification.
USCIS maintains a website to help employers comply with I-9 requirements. As USCIS states, employers must complete an I-9 for each employee hired in the United States and verify the employee's identity. USCIS notes that employers do not file form I-9 with the government. Instead, employers must retain the form for three years and make it available for government inspection.