There's been lots of talk about US authorities prosecuting Julian Assange of WikiLeaks, but it has posed a big question: Assange did all his leaking while remaining outside of the United States, so is it constitutional to extend America's criminal laws to activities beyond its shores?

It's well established that the due process clause places limits on such sweeping assertions of power. For example, when foreign monopolies manipulate prices overseas, it's not enough to show that they have hurt American consumers. Courts insist on evidence that they had fair notice that American anti-trust laws would govern their activity.

Up to now, these constitutional requirements have been developed most elaborately in anti-trust and other areas, which involve civil damages, not criminal punishment. But due process is even more important in criminal procedure, where the Constitution has always held America to more demanding standards.

This basic point has been missed because cases like WikiLeaks are relative novelties. During the first two centuries of the American republic, the justice department only prosecuted extraterritorially for crimes involving recognition that American law was in play – offences that involved direct dealing with the American government or crimes like piracy that were universally condemned by all nations. It was only in the 1980s, and especially since 11 September 2001, that the United States has increasingly used the criminal law as a weapon abroad.

As a consequence, courts are only beginning to grapple with the fair notice problem. In 2003, for instance, the second circuit considered whether due process allowed the United States to prosecute Ramzi Yousef, a non-citizen, for hijacking a Phillippines airliner en route to Japan. The court allowed the proceeding to go forward: given that Yousef's hijacking was a test run for a similar attack he planned for the United States, he should have "reasonably anticipate[d] being haled into court in this country".

But, on the surface at least, Assange could not be charged under a similar rationale. He does not seem to be planning to enter the United States anytime soon. His actions undoubtedly damaged the interests of the United States, but this is true of countless foreigners who release information about America in foreign countries. Surely, it would be unconstitutional for American criminal law to threaten prosecution against every foreigner in the world who denounces the United States?

The Espionage Act of 1917 is the most frequently cited authority for a criminal prosecution. In its 90-year history, it has only once been used against a foreign citizen for an extraterritorial violation. That was in 1985. The case involved Alfred Zehe, who had transmitted classified information about US anti-submarine warfare to the East German government. In defending himself in court, Zehe did not raise any constitutional objections, and so the district judge did not consider them in convicting him. Since Zehe didn't appeal, no higher court has ever ruled on the crucial due process questions.

But that doesn't mean that the justice department should proceed as if the due process clause didn't exist. Unless it can uncover clear and convincing evidence that Assange could reasonably foresee liability under American law, it should not give way to the passions of the moment and launch a criminal prosecution.