Is it conceivable that states, like a child who, denied by one parent, asks the other to let them stay up late, ask around for permission to do something they would not normally be permitted? Lord Atkin enlisted the threat of such a course of action as an argument in his famous opinion for the Judicial Committee of the Privy Council in The Labour Conventions Reference, writing (at p.9 in the document linked to) that “it would be remarkable that while the Dominion could not initiate legislation however desirable which affected civil rights in the provinces, yet its government … need only agree with a foreign country to enact such legislation.”
The judgment, denying Parliament the ability to enact social legislation it felt was necessary to respond to the Great Depression on the ground that such legislation was for the provinces to adopt, made a lot of people furious and, if I remember well, F.R. Scott for example criticized this suggestion as being fanciful fear-mongering. Justice Holmes, writing for the majority of the Supreme Court of the United States in Missouri v. Holland, 252 U.S. 416 (1920), a case that presented much the same issue as Labour Conventions, did not even consider this question, and went on to hold – contrary to Lord Atkin and the Privy Council – that the federal legislature could legislate to implement an international treaty regardless of its (dis)ability to enact the same legislation in the absence of a treaty.
But recent developments suggest that Lord Atkin’s worry it is not so crazy anymore, if it ever was. On intellectual property for example, states (and supranational organizations such as the European Union) have apparently taken to using free-trade agreements as vehicles for smuggling into their domestic legislation restrictive rules on intellectual property which they would might find politically impossible to enact in stand-alone statutes visibly devoted to this purpose, as University of Ottawa’s Michael Geist has detailed in a series of blog posts.
Of course, there is a crucial difference between this example and the Labour Conventions case. The impediments to legislative expansions of IP rights are (mostly) purely political, not constitutional. In such cases, Lord Atkin’s “watertight compartments” (p. 10) are of no assistance. Nonetheless, his insistence that the existence of an international treaty should not prevent us from insisting that the usual constraints, be they constitutional or political, on government power ought always to be be upheld. Foreign governments should not be able to play the lenient parent if domestic courts, or voters, are inclined to be strict.