Path to judicial activism? The use of “relevant rules of international law” by the WTO Appellate Body

The Appellate Body (AB) of the World Trade Organization (WTO) is currently under the concrete threat of ceasing its activities in the near future. This is the result of a series of unaddressed criticisms by some of the members of the organization, in particular the United States, regarding the alleged activist role that the AB has played. These criticisms comprise a number of issues regarding interpretative practices developed by the organ. Against this backdrop, the present paper addresses the use of “relevant rules of international law” which are external to the WTO covered agreements, in particular through Article 31(3)(c) of the Vienna Convention on the Law of Treaties (VCLT), the provision codifying the so-called “principle of systemic integration”. It studies the reports where reference to this provision was made and whether non-WTO rules have been used in an expansive or limited way with respect to the mandate of the AB. It also assesses the reception of these reports by the WTO membership in the meetings of the Dispute Settlement Body. It is concluded that, while recourse to external sources under the VCLT provision could represent a potential source of expansion of the AB applicable law in a way that could displease parts of the WTO membership, the organ has shifted from a progressive approach, which marked the beginning of its functioning, to a more narrow approach of the applicability of non-WTO sources in the more recent case law.