This field is used to define the tax rule to be applied to the invoice. This information is controlled by the BP tax rules miscellaneous table.
Only one tax rule with a legislation and group that are consistent with those of the document can be entered. See the documentation on general principles linked to the mutli-legislation setup.
From this field, you can:
If this information has been modified, the taxes is automatically re-calculated.
The parameter CTLTAX - Tax codes control (VEN chapter, VAT group) is used to control that the BP tax rule: