Further,as from 1 January 1958 or the earliest practicable date thereafter, contracting parties shall cease to grant either directly or indirectly any form of subsidy on the export of any product other than a primary product WHICH subsidy results in the sale of such product for export at a price lower than the comparable price charged for the like product to buyers in the domestic market.
It's an official WTO article. I'm confused of the WHICH here. I thought it should be a WHOSE. Is it an adjective clause?