Tax code field on line items

I need a quick assist.  I have a couple of AR operating units set up.  On the new one I just set up, when I try to enter an invoice, the tax code on the line items is a required field.  On the older orgs it is not.  I know there must be a check box somewhere in the setup that controls this but so far this morning i have not been able to find it.  Since we don't use tax for the new org, i don't want it to be a required field. 

We are on apps 11.5.10.2.  Any help on a Friday morning would be much appreciated.