It's not a matter of "legal" requirements--the law does not mandate background checks or say what should be part of them. It's a matter of the two parties (the consultanting company and the client) want and can agree to. Your client doesn't need to hire you--they choose to. Since it is purely voluntary whether to hire your firm (or any firm), they can say what information they want. You are free to say you will not provide it, since no law forces you to work with them..,and they in turn can refuse to hire your firm. It's like with an individual's employment: the employer can decide what its terms of or requirements for a job are, and an individual can decide whether to take that job or not.You and the prospective client, being free to enter into (or not) a relationship, have to work it out between you. And if you are to uncomfortable with these demands (which is not unreasonable: social security numbers, for example, are sensitive information), you may need to walk away.