If you're interviewing potential employees there is a list of questions you should be careful NOT to ask during a job interview or in the job application, UNLESS it is somehow related to the job at hand.
As a California employer you want to be fair to all your prospective employees, and to help prevent unfairness CA passed the California Fair Employment and Housing Act (FEHA - CA Gov. Code Sec. 12940 et seq.), which prohibits discrimination against current employees and applicants on the basis of:
The policy behind FEHA is that these characteristics should NOT play a role in whether an applicant can perform the job at hand, therefore they should not be asked directly and for no reason. But if the characteristic is related to the ability to perform the job, it's better to ask a general question about the ability to perform the job. For example, if you suspect the applicant is pregnant and the job requires heavy lifting up to 75 pounds, you should simply ask whether the applicant can lift items up to that weight, and not whether the applicant is pregnant.
Remember, FEHA was passed to prevent discrimination, so you need to make sure that the applicant or employee does not feel your treatment of them or decision not to hire them was based on any of the above characteristics. And the best way to protect against the potential perceived discrimination is to avoid focusing on the characteristic. Also keep in mind that a diverse workplace breeds more productivity and profit.
*This material is intended for general information purposes only and does not constitute legal advice. Each case requires unique legal analysis of law and facts. For legal issues that arise, the reader should consult legal counsel.