New job asking for credit documents.?

Just got a new job offer, got all paper work and start date. They ran a credit check and then retracted the offer unless I can prove I'm working with the creditors. I'm doing it, but I can't shake the fact a new job is asking for private letters and documents between me and my credit cards. If it will get me the job, I will do it, but it seems like an invasion of privacy. Can they do that?