Credit Check in SO

Hi Experts,

My client receives third party Gaurrenty from Customer for the payment of bill.Client is using credit check functionality in SAP. However to avoide the credit check in relation to Order's of customers who have provided the TPG we madethe cofig. of Gaurrenty and assigned the fin. docu. to So.

When SO with Fin Docu.No is process the credit check was not made for the amount of that SO. (Normal process when fin docu. is asigned)

How ever when client removed the Fin Docu. no from SO and processed the SO the credit check was not performed.

Client want's that if the Fin Docu. is removed from the SO then credit check should be performed for that SO

Can any one guide me how this could be achieved?

Thanks

JS