Rita Risser responds:

Legally you are required to ask every applicant (not just "obvious foreigners") these questions: "Are you legally entitled to work in the U.S.? What is your visa status?" Upon hiring, the applicant must complete an I-9 form and provide proof of legal entitlement to work here, such as a passport, green card or other documentation spelled out on the form. It is not legal to ask, "Are you a U.S. citizen?" unless the job requires a Department of Defense security clearance. If the job requires access to "high technology" such as encryption, the Export Control law requires screening applicants who are citizens of certain countries, and obtaining licenses for them from the Dept. of Commerce to have access to that technology. If you are such an employer, contact an attorney to set up an appropriate system.