How can I check if there's open PO to match an invoice?

Hi all,

I have the following scenario...

We're in Brazil and here we have Integrated Receiving (RI), which is a module specific to calculate Brazilian taxes. So, we do all receiving through RI and not through PO.

Today, we have a lot of invoices that we receive that doesn't have a PO attached. So, we decided to control this on the arrival of the invoice.

So, when the carrier comes with the invoice, the person on the lobby will check this invoice and see if there's a PO created for it, checking the values and if there's balance for it. If it doesn't have any PO for it, they can't receive the items nor the invoice.