We state in Just Trade that "no legal impediment" requires the PPM distinction. Columbia University's noted trade economist, Dr. Jagdish Bhagwati, has confirmed in the Foreword to the first issue of the Indian Journal of International Economic Law, that legal interpretation did not enter into the equation. Jagdish recalls, as the GATT Director General’s Economic Policy Advisor, being drawn into the discussion of what the panel should be asked to do about the creative U.S. claim that GATT article III permitted its discrimination among tuna imports based on how they were harvested. He notes that the decision was based on two factors: first, that PPMs could too easily be used as disguised protectionism. For example, a developed country could deny access to its market of products from Members that did not pay their workers a fair wage.
As we note in Just Trade, this basis is ironic, given the rich interpretive history of GATT Article III, which offers stronger discipline against disguised protectionism than any other WTO provision.