The US Justice Department has rescinded an Obama administration policy that had eased enforcement of federal marijuana laws in states that have legalised the drug, instead giving federal prosecutors wide latitude on pursuing criminal charges.
Attorney General Jeff Sessions, known as a strong opponent of legalising marijuana, overturned the policy but stopped short of directly encouraging prosecutors to bring marijuana cases.
His action drew immediate condemnation from marijuana legalisation advocates and some lawmakers in both parties who said it trampled on the rights of voters in states where the drug is now legal and created uncertainty about how strictly federal drugs laws will be enforced.
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The administration's move also raised questions about how the new policy will impact the burgeoning marijuana industry in places like California and Colorado.
The policy put in place under Democratic former President Barack Obama, outlined by then-Deputy Attorney General James Cole, recognised marijuana as a "dangerous drug," but said the Justice Department expected states and localities that authorised various uses of the drug to effectively regulate and police it.
"The Cole memo, as interpreted, created a safe harbour for the marijuana industry to operate in these states, and I think there is a belief that that is inconsistent with what the federal law says," said a Justice Department official who briefed reporters on condition of anonymity.
"Marijuana is still against federal law."
Under the new policy, outlined in a one-page memo by Sessions, federal prosecutors around the country will have discretion to enforce the federal ban on marijuana in their own districts.
The change under Republican President Donald Trump's administration comes just days after California formally launched the world's largest regulated commercial market for recreational marijuana.
Other states that permit the regulated sale of marijuana for recreational use include Colorado, Washington, Oregon, Alaska and Nevada. Massachusetts and Maine are on track to follow suit later this year.