Can we hide or remove the "Tax Exempt" field on the initial voucher input page?

We are using Payables 9.1 MP2.  We are having issues with the consistency of data being input into the sales and use tax fields in a voucher and are thinking about making them required fields.  In order to do that, we need to eliminate the "Tax Exempt" flag from the initial voucher input page but can't seem to see where to control that field.  Can anyone point us in the right direction?

Regards, Mark