How to stop a credit memo for more than the reference invoice?

Hi All,

My company would like to stop users from creating credit notes for more than the original invoice value, when the credit memo is referenced to an invoice. E.g. invoice is for $100, then multiple credit notes can be created, e.g. for $50, $30, and $30. Total credited = $110, but the original invoice was only for $100.

there doesnt seem to be a standard message which can be issued under these circumstances in order to stop the users from doing this. Does anyone have any advice on how to stop this?

Many thanks

Phil