Restrict/Disable Reject option at line level acknowledgement on iSupplier page

Hello,

There is a requirement to not allow supplier "Reject" a Purchase order line during acknowledgement process via isupplier portal. Using personalization the "Reject entire order" button has been disabled. However at the Shipment line level, there is still an option to Accept / Change / Reject.

Any ideas on how to restrict/remove the "Reject" option at the Shipment level as well.

What is the source LOV table for this field ?

Navigation: iSupplier responsibility - Orders (tab) query a purchase order - Choose Acnowledge & Press Go - Expand to PO shipment lines - Choose Accept, Change or Reject the Shipment line (See attached image)