Reasonable interview questions have to do with the job and don't assume what kind of worker you will be because religion, race, sex, age or national origin (where your family is from). In some states, there are stronger protections for other types of people.
It may show that they are discriminating when they don't ask all applicants the same questions (only asking women about child care or people with accents where they are from).
Questions about age Employers should not judge workers by their age and asking how old you are could show discrimination. Questions which give pretty good clues about your age, like asking when you graduated, are suspicious. They shouldn't ask how much longer you plan to work. The only question that's ok is "are you are at least 18 years old" (if there are state laws on youth employment).
Questions about medication Many bosses ask if you're taking any medication, which is a problem when you don't want to tell about medications which will tell them about a medical condition. The only question which should be asked is "are you taking medication that could affect your ability to do this job?" No matter what question they ask, you only have to answer about medication that could affect you on the job.
Once you have been offered the job, employers have more rights to get medical information (but they should be getting the same information from every employee). They can withdraw the job offer based on your medical history or medications you're taking, if it could affect your ability to do the job or if you didn't give accurate information. They can't withdraw a job offer because you are HIV positive.
Questions about unions Asking you if you are a union member or if you support unions could be suspicious. If you are asked, you have no responsibility to answer honestly. You might want to say you don't know very much about unions, even if you do. They can tell you what they think about unions: "there's no union here and we want to keep it that way." Just say that you understand and remember that workers decide if there's a union, not the company.
Questions about your religion Asking what religion you practice or how you practice it can be a sign of religious discrimination. It is ok for an employer to explain the requirements of the job and ask if you can meet them (for example, "this job includes working on Saturday and Sunday. Is that a problem?"). You have some rights to ask for accommodations to practice your religion after you have the job.
Questions about a disability Asking if you have a disability is one of the only questions that is actually illegal to ask. They can ask "are you able to perform each of the job requirements, with or without an accommodation?" Even if you will need an accommodation for a disability, you don't have to tell them before you are hired that you will need an accommodation.
Questions about work injuries If you are asked if you've ever had a work injury or filed a workers' comp claim, they could be trying to find out if you have a disability. Of course, they could also be trying to find out if you're a worker who knows their rights to workers' comp.
Questions about where you are from Asking "what country are you from?," "what is your native language?," "have you changed your name?," or "were you born in the U.S.?" suggest that the employer wants to know about your "national origin." The only thing they should be asking is if you will be able to show that you can work in the U.S. or what languages you speak.
Questions about children and childcare It's very common for bosses to assume that parents, especially women, will be distracted or need time off. You shouldn't be asked how many children you have or if you're planning to have kids. All they should ask is if you can meet the requirements of the job, after describing scheduling and overtime needs.
Questions about criminal history It is usually very hard to find a job if you have a criminal record. It can show discrimination when employers won't hire any workers with criminal histories, since a higher percentage of minorities have a record. Some states set limits on the questions that can be asked, depending on the type of crime and how old it is. Generally, bosses shouldn't ask "have you ever been arrested?" (since you weren't found guilty of anything). The most legitimate questions about criminal history are when they pertain to the job (like an accountant job when you've been convicted of embezzlement).
Questions that aren't about the job Questions about personal things that aren't related to the how well you can do the job often make problems. Personal information makes it more likely that bosses will want to hire the person most like them (for example, if they ask what clubs or social groups you are in, instead of asking if you are active in any professional organizations).
Questions that are ok to ask The most common questions are: your name, address, Social Security Number, the kind of job you want, your current employer and job, whether they can contact your employer, your salary, reason for leaving old jobs, military service, references, contact information, and emergency contact information. They can also ask if you will be able to do each part of the job (lift boxes, drive a truck for a certain number of hours, stand for long periods, work weekends as needed, etc.). The only reason to ask you personal questions is if it's related to the job, called a "Bona Fide Occupational Qualification" (BFOQ) or because of a legal, formal plan to monitor how many minority employees there are.