Yes. In fact, it is a violation of the federal Fair Debt Collection Practices Act for a debt collector to contact you at work if your employer disapproves and they are informed of this fact by you or your employer.

You or the employee can tell the debt collector to stop. Simply interrupt him and say, “This is my work number. Do not call me here again.” And then hang up. 99% of the time, that will take care of it.