According to the anti-discrimination provision of the Immigration and Nationality Act (INA), employers can't discriminate against potential employees based on their immigration or nationality status. Asking which specific types of documents applicants will use to verify eligibility puts you at risk of facing a discrimination lawsuit under the INA.
So you shouldn't ask an applicant which documents they have to prove authorization, but you can inquire as to whether or not an applicant will require an H1-B visa, for instance. Be sure to ask the same question to every applicant.
The US Department of Justice's Office of Special Counsel (OSC) for Immigration-Related Unfair Employment Practices is responsible for enforcing the anti-discrimination provision of the Immigration and Nationality Act.
The OSC has previously established the following questions are allowable in an interview setting:
In this way, you can ask if an applicant will need an H1-B visa, without directly asking them which documents they have.
The Equal Opportunity Commission (EEOC) recommends adding the following statement to employment applications to ensure compliance:
"In compliance with federal law, all persons hired will be required to verify identity and eligibility to work in the United States and to complete the required employment eligibility verification document form upon hire."
FAQs - justice.gov Frequently Asked Questions about the OSC