The job interview is an essential component of the hiring process, but asking the wrong questions could result in undesirable and costly litigation. 
The job interview gives the applicant and the company  a chance to assess whether the company  and the applicant will be well suited. 

Interview Preparation

Begin by having a set of prepared questions . 

Consider the legality of those questions before the interview. If you are uncertain, don’t ask the question. 

Keep the interview focused on job related questions. Even if the applicant  offers   personal and not job related questions, redirect the interview back to the job and it’d duties.

Questions which you have already  considered the legality of.

file:///C:/Users/lao12/Desktop/Legal-Illegal-Interview-Questions.pdf

: An interviewer represents the company, and job candidates will perceive any interview encounter as “acceptable college practice”. Therefore, as you prepare your interview questions, ask yourself: • Is the question legal? • If it is legal, is it appropriate? • When in doubt, don’t ask. Focus on the job-related information.

Please note: Every interaction with the candidate constitutes part of the interview: phone conversations, transport to and from a hotel, meals, walking across campus, etc. Everyone who will have contact with candidates should therefore be made aware of areas of inquiry that are not appropriate or illegal questions that should not be asked.

If a person volunteers information that is not job related, direct the conversation back to job-related topics. Information volunteered by an applicant that is not job-related – especially information about a job applicant’s protected status (see below) – should not affect your decision about the applicant’s ability to do the job. Refer difficult questions and issues to Human Resources.