the "Purchasing" flag at the supplier site level.

The "Purchasing" flag at the supplier site level. When this flag is unchecked, the site is not intended for standard purchasing transactions (i.e., generating purchase orders). However, suppliers are still able to participate in tenders (negotiations) even if this flag is not checked.

How can we prevent the supplier from participating in the tender if the "Purchasing" flag at the supplier site level is not checked?