Citizenship perhaps not, but it's not at all illegal to ask whether a prospective employee is legally able to work in the United States, and upon hire it's requ

Citizenship perhaps not, but it's not at all illegal to ask whether a prospective employee is legally able to work in the United States, and upon hire it's required to demand documentation to prove it. The form is called the I-9. https://www.uscis.gov/i-9 https://www.uscis.gov/i-9