Article 3.2 of the World Trade Organization DSU requires panels to clarify existing provisions of agreements in accordance with customary rules of interpretation of public international law. This leads to consideration of how the NVNB principle interacts with Article 26 of the Vienna Convention on the Law of Treaties, incorporating the principle of pacta sunt servanda: "Every treaty in force is binding upon the parties to it and must be performed by them in good faith." NVNB claims appear to undermine this fundamental principle of international law by subsequent reinterpretations based on the 'spirit' of the agreement.[1]