requiring an invoice and w-9 from the repair shop before the

My lien holder on my automobile is requiring an invoice and w-9 from the repair shop before they will endorse the check and send it only back to the repair shop not me. Is this legal for them to do this? And why does the shop have to send a w-9?

I had the wreck on 9/29/10. The insurnce came out and give an estimate on 9/30/10. I mailed the check and estimate to my lien holder certified mail that same day. I don't know any company that is going to repair first then get paid later. I could be without my car for far longer than I had planned if this is how I have to do it.