A United Nations panel responsible for enforcing anti-drug treaties just issued a stark warning to the U.S., Canada and other countries where marijuana legalization is being considered and enacted.

Countries are prohibited from legalizing cannabis — except for medical and scientific purposes — under three drug control conventions enacted in 1961, 1971 and 1988.

But that hasn’t stopped a growing number of U.S. states, and some entire nations, from moving to end marijuana prohibition. Eight states have now legalized cannabis, as has the country of Uruguay. Canada’s government has pledged to introduce a plan to legalize and regulate marijuana this spring.

The International Narcotics Control Board (INCB) isn’t happy with these developments, and is doing its best to put the brakes on such reforms.

“In its discussions with the Government of the United States, the Board has continued to reiterate that the legislative and administrative measures taken by several states in the country to legalize and regulate the sale of cannabis for non-medical purposes cannot be reconciled with the legal obligation” under the international treaties, a new INCB report released Thursday says.

Similarly, INCB reveals that its personnel visited Canada last fall: “The primary objective of the mission was to discuss legislative measures currently being developed relating to the legalization and regulation of the nonmedical use of cannabis,” the board writes.

“The limitation of the use of drugs to medical and scientific purposes is a fundamental principle that lies at the heart of the international drug control framework, to which no exception is possible and which gives no room for flexibility. The Board urges the Government to pursue its stated objectives — namely the promotion of health, the protection of young people and the decriminalization of minor, non-violent offences — within the existing drug control system of the Conventions.” [Emphasis added.]

And although the treaties do allow legalization of medical cannabis, INCB isn’t exactly happy with how it’s being done in U.S. states:

“The Board also remains concerned that many of the legal and regulatory frameworks of the states that permit the use of cannabis for medical purposes do not fully comply [with the treaties]… All Governments that have established programmes for the use of cannabis for medical purposes, or that are considering such initiatives, are reminded of their reporting and licensing obligations under the international drug control treaties. Such programmes must ensure that the prescription of cannabis for medical purposes is performed with competent medical knowledge and supervision and that such prescription is based on sound medical practice.”

But even while opposing legal regulation of marijuana markets, INCB is now on board with simple decriminalization of possession of cannabis and other drugs: “The Board encourages States to adopt nonpunitive responses for minor drug-related offences committed by drug users, instead of arrest and incarceration, as an alternative provided by the international drug control conventions.”

Though INCB is clearly upset with recent marijuana reform developments, its enforcement activities are generally limited to public finger wagging and the issuing of critical reports, so it is unclear to what extent nations and states will feel pressure change their plans in response to the new document. Similar reports in the past don’t seem to have slowed the legalization movement from continuing to gain momentum.

But to the extent that countries do take INCB’s threats seriously, they have a few options. The U.S., for example, can argue that it is still in compliance with the drug control treaties because marijuana remains illegal federally despite anti-prohibition laws enacted by a growing number of states. Under the U.S. Constitution, the federal government cannot force states to enact or enforce drug prohibitions.

But Canada’s national legalization plan will likely put the country in direct conflict with its obligations under the conventions. The country could withdraw from the treaties or, perhaps more likely, it could attempt to frame its legalization of cannabis for all adults as falling under the medical and scientific exceptions. For example, the government could argue that moving marijuana out of the criminal market is a harm reduction measure that will improve health outcomes for consumers by allowing the kind of testing and labeling of products for potency and purity that is not possible under prohibition. The country could also collect data on legalization outcomes, in effect framing the end of prohibition as one big scientific study.

Canadian Health Minister Jane Philpott told senators on Wednesday that she’s had conversations with officials from several other countries who are eager to see what her government does, perhaps as a model for how they too might move toward legalization.

“They’re watching Canada very closely, which speaks to the fact that we have got to get this legislation right,” she said.

Philpott reiterated the government’s pledge to announce its legalization plans this spring, which begins March 20 and ends June 21.