I wrote last summer about the issue whether a federal legislature could enact a statute in order to implement a treaty despite the fact that, absent the treaty, the statute would be ultra vires (because provincial or state, rather than the federal legislatures have jurisdiction over its subject matter. If so, I said, this would give states the ability to act “like a child who, denied by one parent, asks the other to let them stay up late,” with other states playing the role of the lenient parent. I think that, in public policy (as, I suppose, in parenting) this is a bad idea. And, in Canada, the constitution has been interpreted as preventing such schemes, in the Labour Conventions Reference.
The leading case on this issue in the United States is Missouri v. Holland, 252 U.S. 416 (1920), I always thought that it stood for the contrary proposition, that Congress can legislate to implement a treaty regardless of whether its subject-matter is within its enumerated powers. But now people better-informed and wiser than I, namely Nick Rosenkranz and NYU’s own Rick Pildes, will take up the question of whether this is right over at the Volokh Conspiracy, in anticipation of, maybe, the US Supreme Court eventually hearing a case where it arises. (Their first stab at it is here.)
It should be very interesting, and too much for any effective summary here, so I thought I’d alert however many (or, more likely, few) readers I have.