They can be explicitly requested by the employer or required by the law. I had to provide the criminal background and prove my studies to my current employer.

They can be explicitly requested by the employer or required by the law. I had to provide the criminal background and prove my studies to my current employer. I also had to pass a medical examination to obtain a certificate of eligibility to work. They are provided by the applicant anyway, you don't do secret background checks, at least you shouldn't.