I am not a lawyer, but having worked in a corporate setting for years this is something that's drilled into us constantly. Edit: A bit of searching leads me to

I am not a lawyer, but having worked in a corporate setting for years this is something that's drilled into us constantly. Edit: A bit of searching leads me to the Civil Rights Act of 1964 (https://en.wikipedia.org/wiki/Civil_Rights_Act_of_1964 https://en.wikipedia.org/wiki/Civil_Rights_Act_of_1964). I'm not sure if the wording specifically prohibits asking about protected statuses, but any legal decisions about that would probably have their roots in that Act.