Ask the wrong questions during a job interview and you could end up with a poor performer or, worse yet, open yourself up to a lawsuit. Employers are prohibited from using characteristics such as age, race, gender, disability, religion, veteran status, or sexual orientation, etc., in employment decisions.

But when it comes to interviewing, it can be a fuzzy line; it’s not always easy to know what constitutes an inappropriate question. As a result, seemingly innocent questions posed during a job interview can lead to charges of discrimination in the workplace. Yet, with a few exceptions, merely asking about these issues is not illegal. Here’s the tricky part: Such questions may imply an illegal motive, and they can be used as evidence of discrimination. That’s why you want to avoid them.

What are the exceptions? Here are three significant questions that are illegal:

• The Americans with Disabilities Act prohibits asking about an applicant’s mental or physical disability.