Here is the entirety of the WTO Seal Products panel's GATT Article III:4 analysis:
220.127.116.11 Analysis by the Panel
7.604. Article III:4 of the GATT 1994 provides that:
The products of the territory of any Member imported into the territory of any other Member shall be accorded treatment no less favourable than that accorded to like products of national origin in respect of laws, regulations and requirements affecting their internal sale, offering for sale, purchase, transportation, distribution or use.
7.605. There are three elements that must be examined to assess a measure's consistency with Article III:4 of the GATT 1994: (i) whether the measure is a law, regulation or requirement affecting the internal sale, offering for sale, purchase or use of goods; (ii) whether the products at issue are like; and (iii) whether imported products are accorded less favourable treatment than that accorded to like domestic products.937
7.606. With respect to the first element of Article III:4, we note that the EU Seal Regime is undoubtedly a "law" or "regulation" affecting the internal sale, offering for sale, purchase, distribution and use of seal products within the meaning of Article III:4.
7.607. As regards the second element of Article III:4, we found in the context of Canada's claims under Article 2.1 of the TBT Agreement that seal products are "like" irrespective of whether they conform or not to the requirements under the EU Seal Regime. We also recall that the parties do not dispute that conforming and non-conforming seal products are like.
7.608. With respect to the third element under Article III:4, the national treatment obligation contained therein requires that imported products from Canada and Norway receive a treatment no less favourable than that accorded to domestic seal products.938 Based on the evidence before the Panel, it appears that the vast majority of seal products from Canada and Norway are excluded from the EU market by the terms of the MRM exception.939 In contrast, evidence shows that virtually all domestic seal products are likely to qualify for placing on the market.940
7.609. In light of the above considerations, we conclude that the measure at issue grants Canadian and Norwegian seal products a treatment less favourable than that accorded to EU seal products within the meaning of Article III:4 of the GATT 1994.
That's 6 total paragraphs, only one of which addresses less favorable treatment. And if I'm reading that paragraph, 7.608, correctly, it basically says that a disparate impact on imported goods is enough to find a violation.
To be fair, the panel fleshed out this part earlier in the context of the TBT 2.1 analysis and in a section on the relationship between the GATT and the TBT Agreement. But nevertheless, this seems to be a fairly low hurdle for finding a violation of GATT Article III:4.
Is this the right approach? What will the Appellate Body have to say about it?