There are many things an interviewer can ask a job applicant. But, you do need to be careful about some questions. Here are some things to consider.
1. How old are you? Be very careful about asking this question. There are very few jobs where someone can ask you your age and the question itself not serve as evidence of age bias. It is best to not go there unless you are hiring for jobs with clearly appropriate age requirements, such as the US Army.
2. Are you married? If you ask this only of female applicants, then this question could cause you problems. Why would this question be helpful? Unless this is a ruse to discover whether a female applicant might quit when she wants to have a baby. This question serves little purpose.
3. Are you a US citizen? It would be best to not ask this question until a job is offered. This question could conflict with the Immigration Reform and Control Act of 1986. It could also serve as evidence in an ethnic origin case, if the question is only asked of Hispanic or Hispanic-appearing applicants.
4. Do you have a disability? Do not ask this specific question. But, an employer can ask something similar if an applicant has any limitations that would keep him/her from performing essential functions of the job. How else would a fire department make sure an applicant can carry someone out of a burning building? So, yes you can ask about physical or mental limitations that would impair the performance of the essential functions of the job. But, do not ask about disabilities or diagnoses until a job offer has been made.
5. Do you take drugs, smoke or drink? An employer can ask about drinking, smoking or illicit drug use. An employer should not ask about legal or prescription drug use, since that might involve issues of a possible disability.
6. What religion do you practice? An employer cannot ask about religious practices. Since, that could be used as evidence later of religious discrimination.
7. What is your race? No, of course, this would be an inappropriate question. See No. 6 above. Don’t we all know not to ask this by now?
8. Are you pregnant? This question could be used as evidence of female stereotyping and, therefore, as evidence of gender bias. So, it is better not to ask this question. And, as the article mentions, refusing to hire a woman based on pregnancy or possible pregnancy would violate the Pregnancy Discrimination Act.
All of these warnings only matter if some adverse personnel action occurs later for which there is no otherwise reasonable explanation. If an employer asks about pregnancy and then later fires the applicant for some trivial transgression, only then would questions asked in an interview have any relevance. A discrimination lawsuit requires first and foremost a negative personnel action with no otherwise reasonable explanation. The lack of an otherwise rational explanation for an adverse personnel action is what makes prior discussions possibly relevant. The best defense for any employer is to simply issue written warnings whenever a transgression occurs. Emphasizing written discipline, applied consistently will serve the employer very well.