On SSRN, Professor Michael Paulsen has posted "The Constitutional Power to Interpret International Law." An extract from the paper:
What, then, of international bodies’ interpretations of international law, including international treaties to which the United States is party—such as the U.N. Charter, the Geneva Conventions, and the Convention Against Torture? Are international bodies’ (like the International Court of Justice’s) interpretations of these international treaties binding on the United States?
It follows from what has already been discussed that the answer must be no. As a matter of U.S. constitutional law, the interpretation of U.S. law, including U.S. treaties, cannot be authoritatively or finally vested in non-U.S. authorities. Such persons or bodies possess no part of the Constitution’s authority. They are not officers of the government of the United States, within the meaning of that term as used in the Constitution. They are certainly not Article III judges. Their decisions may not govern the United States. Nor may U.S. government actors cede their constitutional powers to such persons or entities. U.S. officials of course may consider what international organizations or courts have to say about America’s international obligations. And surely the President may contract (by treaty or by executive agreement) with other nations to agree to submit certain disputes to resolution by international or neutral authorities, and thereby create international and moral obligations. But no such agreement literally may dictate or control the actions of U.S. government authorities. It follows that no decision of an international tribunal or court may be self-executing—binding on U.S. executive, legislative, or judicial authorities— consistently with the Constitution, unless U.S. law (self-executing treaty or statute) both makes it so and makes it so in a fashion permitted by the U.S. Constitution.
Thus, Professor Paulsen takes the position that the interpretations of international tribunals are not "binding" on the United States. (In the WTO context, many people will recall the well-known exchange between Judith Bello (whose article is not online as far as I can tell) and Professor John Jackson (whose article is online here:(http://www.asil.org/ajil/v9160.pdf ) on similar issues.
I find some aspects of the discussion of whether international decisions are "binding" confusing. I'm often left unsure about what people are saying exactly. I suppose it may depend on what is meant by "binding." Does calling an international decision (and the interpretations therein) "binding" mean that there is a mechanism to force the United States (or other countries) to follow the ruling of the international tribunal? If so, then the interpretations of these tribunals are probably not binding, because there is no way to force compliance (although there are, in some international agreements, mechanisms to encourage compliance). So in that sense, an interpretation by an international tribunal is not "binding."
On the other hand, "binding" could also mean that the interpretation offered by the tribunal is formally part of a treaty's body of law. Thus, for example, under the DSU, panels and the Appellate Body interpret (technically speaking, they "clarify") the WTO agreements. Are these clarifications "binding" in the sense that they become a formal part of WTO law, which the United States has agreed to follow? I would say the answer is yes.
Based on the above quote, however, I'm not completely sure what Professor Paulsen's view is on this. At one point he says, "As a matter of U.S. constitutional law, the interpretation of U.S. law, including U.S. treaties, cannot be authoritatively or finally vested in non-U.S. authorities." That makes me think his answer would be a clear no. But later he says "no such agreement literally may dictate or control the actions of U.S. government authorities"; and, "It follows that no decision of an international tribunal or court may be self-executing—binding on U.S. executive, legislative, or judicial authorities"; and also, "And surely the President may contract (by treaty or by executive agreement) with other nations to agree to submit certain disputes to resolution by international or neutral authorities, and thereby create international and moral obligations." These statements make me wonder if he has something more limited in mind. For example, perhaps his view is that interpretations by international tribunals can, in fact, be part of international law as part of that law in and of itself; however, they cannot be part of that law as it is incorporated into domestic law. Thus, taking the WTO context as an example, interpretations by the Appellate Body could be part of the WTO law that is applied by panels and the Appellate Body in future WTO disputes. However, they cannot play the same role in U.S. law as the WTO Agreement itself does. That is to say, international agreements play a special role in domestic law, and international decisions interpreting the agreements do not play this same role. (If I recall correctly, this is the view taken in recent years in some U.S. Court of International Trade decisions.) If he does take this latter view, I can see why he argues that the decisions are not "binding" on the United States. That is true, in one sense. But in another sense, they are, as they become part of U.S. international obligations.