approval query for using a specific warehouse on a/r invoice

Hi

Im in need of an approval query that will trigger when a specified originator tries to add an A/R invoice when one or more item lines are invoiced from warehouse called "W03"

our user can create sales orders and invoices from different warehouses and they can invoice from multiple different warehouses on one document, i just need to create an approval procedure for certain users that use "W03" warehouse.

Your help will be greatly appreciated