Could Prime Minister Justin Trudeau's plans to legalize cannabis in Canada become derailed by international treaty disputes? The Canadian Press broke a story earlier this week that has politicians and commentators talking about that possibility. But it could prove to be a rough patch rather than a roadblock.

Legalization has always been framed as a domestic issue. That changed Jan. 5 when the Canadian Press obtained a briefing note prepared for the prime minister. The note warned that Trudeau must prepare to explain to the world how he will legalize cannabis while also conforming to the nation's obligations to international drug treaties, which restrict access to cannabis in Canada to medical use and scientific research.

The United Nations treaties in question are:

According to Errol Mendes, an expert in constitutional and international law at the University of Ottawa, the path to legalization will be a long and hard road for the Liberal government. Mendes told Canadian Press, "It will be an ongoing dialogue which has to be dealt with at the highest levels, and it's not going to be an easy one, and it's not going to be a quick one either. It's going to take many years."

Or maybe not. It's tough to say what will happen given the few precedents for countries that legalize cannabis in defiance of widespread global prohibitions. Right now, the recreational use of cannabis is fully legal in only one country: Uruguay, which has signed the same three drug treaties that Canada also agreed to.

The UN didn't sanction the U.K. for decriminalization

So have the U.N. drug cops invaded Uruguay and put a stop to legalization? No. And they won't because they don't exist.

The three drug treaties are enforced by the U.N.'s International Narcotics Control Board, which has limited powers. (See Article 14 of this Convention.) They can demand an explanation from any country that undermines or fails to uphold the measures of the treaties. They can also call on that country to adopt legal remedies to make its laws compliant with the treaties. And if the country fails to offer a satisfactory explanation and fails to adopt the remedies, they can inform the other nations participating in the treaties and write a report informing the U.N.'s General Assembly of the infraction.

Scary stuff. For an example of this enforcement in action, consider the case of the United Kingdom, which ran afoul of the INCB in 2002 when the Brits reclassified cannabis in such a way that was tantamount to decriminalization. The INCB harshly criticized the move, but the government remained defiant. Indeed, even when the U.K. re-criminalized in 2009, legislators made it clear that they weren't changing their drug laws to comply with the INCB's stance.

They aren't punishing Uruguay either

According to an internal report from 2014, the INCB has begun a dialogue with Uruguay, whose leaders "assured the Board of the Government's commitment to drug control and full and unconditional cooperation with the Board." At the same time, Uruguay moved ahead with legalizing and regulating cannabis. But the dialogue continues as though legalization isn't already well underway in the South American country.

Based on that precedent, it seems that Trudeau can pledge to discuss ways to uphold the treaties, even while breaking them.

The UN's position on cannabis could change soon

But things might not come to an absurd standoff. The U.N.'s position on cannabis could change as soon as this spring when delegates from around the world will meet in New York for the United Nations General Assembly Special Session on Drugs. This event will decide the U.N.'s stance on international drug laws for the next decade. And there's a chance that nations who want the U.N. to soften its stance on marijuana will be heard.

If Canada joins Mexico and other countries calling for a different approach to drug control, it's possible that the dialogue will shift from the U.N. pressuring countries to uphold the conventions, to countries pressuring the U.N. to change the terms of international treaties.

And those delegates could get some reinforcements from the U.S. While pressuring Uruguay to get onside again with the drug treaties, the INBC is also having the same conversation with the U.S. about the states where cannabis is legal. And that conversation could ruffle the feathers of some important politicians. Most Republican and Democratic presidential candidates want to let each state decide the legality of cannabis in their jurisdiction, rather than being told to abide by federal laws - or international ones for that matter.