Credit Check based on payment terms in sales order

Dear Forum,

My client requirement is that i need to block a customer at sales order if the payement terms for example 14 days in sales order is exceeds then it should block at sales order only. I check and find that there is no standard settings in OVA8(Automatic credit check). I think i need to go for user exit or functional module. Kindly let me know the logic and user exit/functional module name in detail. It would be great helpful for me.

Regards

Kishore.