Raymond Yans is president of the International Narcotics Control Board (INCB), the U.N. agency charged with monitoring the implementation of anti-drug treaties. It is therefore not surprising that Yans takes a dim view of marijuana legalization in Colorado and Washington, which he says poses "a grave danger to public health and well-being."

But according to the INCB, legalization is not just dangerous; legalization is illegal. Even Americans who support marijuana prohibition should be troubled by the implications of that argument, which suggests that international treaties trump the Constitution.

In an INCB report issued on Tuesday, Yans scolds the U.S. government for letting Colorado and Washington repeal criminal penalties for production, possession, and distribution of cannabis. "INCB reiterates that these developments contravene the provisions of the drug control conventions, which limit the use of cannabis to medical and scientific use only," he writes. "INCB urges the Government of the United States to ensure that the treaties are fully implemented on the entirety of its territory."

Under our federalist system, however, states have no obligation to punish every activity that Congress chooses to treat as a crime. The Supreme Court has said, based on a dubious reading of the power to regulate interstate commerce, that the federal government may continue to enforce its own ban on marijuana in states that take a different approach. But that does not mean the feds can compel states to help, let alone force them to enact their own bans.

According to the INCB, none of that matters. "The international drug control treaties must be implemented by States parties, including States with federal structures, regardless of their internal legislation, on their entire territory," it says in a recent position paper. "Those treaty obligations are applicable with respect to the entire territory of each State party, including its federated states and/or provinces."

In other words, our government is required to impose marijuana prohibition on recalcitrant states, regardless of what the Constitution says. Can that be true? Only if you believe that international treaties can give Congress authority that was not granted by the Constitution, which would obliterate the doctrine of enumerated powers and the state autonomy that depends on it.

Even if treaties could override federalism, the agreements that the INCB cites do not purport to do so. The 1961 Single Convention on Narcotic Drugs says compliance is subject to "constitutional limitations" and undertaken with "due regard to [signatories'] constitutional, legal and administrative systems." The 1971 Convention on Psychotropic Substances and the 1988 Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances contain similar provisions.

In light of such language, how can the INCB insist that "internal legislation" and "federal structures" have no bearing on a country's obligations under these treaties? "The INCB is just flat-out wrong in making such a claim," says Richard Elliott, executive director of the Canadian HIV/AIDS Legal Network. "The INCB's claim that its narrow, restrictive interpretations of the conventions override domestic constitutional law cannot stand in light of the actual wording of the conventions."

The INCB cites Article 27 of the Vienna Convention on the Law of Treaties, which says "a party may not invoke the provisions of its internal law as justification for its failure to perform a treaty." It also mentions Article 29, which says "unless a different intention appears from the treaty or is otherwise established, a treaty is binding upon each party in respect of its entire territory."

Yet "it's a basic principle of statutory interpretation that a specific statute or command trumps a general one," notes Alex Kreit, a professor at Thomas Jefferson School of law who specializes in drug policy. In this case, the drug treaties make allowances for the constitutional principles that the INCB says are irrelevant.

So is the U.S. government violating international law by letting Colorado and Washington do what they have every right to do? No, and that desperate claim is yet another sign that pot prohibitionists are panicking.