Transportation net amount control

Dears SAPers, We need to control that the sum of the net amount of the deliveries not exceed certain amount (the assurance amount). We need this control when we are creating the shipment (it could be when the deliveries are selected for the shipment).

¿Does anyone knows how we can do this? ¿Does anyone knows if a user exit exist to control this?

I will reward if it helpful.

Thanks in advance!