Employers are legally obligated to make sure that you are authorized to work in the United States. To do this, both you and the employer must complete USCIS Form I-9: Employment Eligibility Verification Form, and you must provide proof of your identity and work authorization. Your employer cannot specify which documents you must present; you can choose any available documents from the lists provided on the form. List A documents (such as a U.S. passport) provide evidence of both identity and authorization to work. List B documents (such as a driver’s license) prove identity, and List C documents (such as a U.S. birth certificate) prove work authorization. For information on the I-9 form -- and the variety of other documents you may be asked to sign as a new employee -- see Nolo's article First-Day Paperwork for New Employees: Understand What You're Signing.