Is it legal to ask a job applicant if she/he is authorized to work in the US?
I'm not sure a job applicant is a US citizen or has working papers and is authorized to work in the US. I do not want to offer them the job if they are not.
You should be concerned here as many states, including CA are cracking down on employers that hire illegals. You should make it a habit that people that come to interview for positions bring their driver's license or passport or some sort of residency proof that you can make copies of. This way, if you hire the person and they lied, you can show the state that you made reasonable efforts to avoid hiring an illegal and that you took necessary steps to prevent it. If you have real concerns, have the employee provide you with proof and send it to the state to confirm that the employee is in fact a US citizen/has working paper. No one can fault you for taking this precaution.