The Wagner Act of 1935, the Equal Pay Act of 1963, the Civil Rights Act of 1964 and multiple Supreme Court decision since then have all contributed to the existence of job interview questions that are illegal to ask. It is worth keeping in mind, however, that it is also illegal to speed in excess in 35 mph on certain roads. The point being that just as you are very likely to see cars breaking speed laws on your way to the job interview, you may very well come face to face with an interviewer who breaks the laws against asking certain questions.