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A budtender displays cannabis at the Higher Path medical marijuana dispensary in Los Angeles, California, December 27, 2017.

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Last Updated Jan 4, 2018 11:53 AM EST

WASHINGTON — Attorney General Jeff Sessions is going after legalized marijuana. Sessions is rescinding a policy that had let legalized marijuana flourish without federal intervention across the country.

That’s according to two people with direct knowledge of the decision. They were not allowed to publicly discuss it before an announcement expected Thursday and spoke on condition of anonymity.

The move will leave it to U.S. attorneys where pot is legal to decide whether to aggressively enforce federal marijuana law. The move likely will add to confusion about whether it’s OK to grow, buy or use marijuana in states where it’s legal, since long-standing federal law prohibits it.

The decision comes days after California began selling recreational marijuana. Today, 29 states have adopted medical marijuana laws. In 2012, Colorado and Washington became the first states to legalize recreational marijuana, and since then, five more states have passed recreational marijuana laws, including Massachusetts, where retail sales are scheduled to begin in July.

States that have already legalized marijuana are likely to protest Sessions’ plan. Colorado Sen. Cory Gardner is already saying that the attorney general is going back on what he’d told Gardner earlier.

He tweeted that this “contradicts what Attorney General Sessions told me prior to his confirmation. With no prior notice to Congress, the Justice Department has trampled on the will of the voters in CO and other states.” 

And he’s also threatening retribution. “I am prepared to take all steps necessary, including holding DOJ nominees, until the Attorney General lives up to the commitment he made to me prior to his confirmation,” he tweeted, along with a reminder that “@realDonaldTrump had it right. This must be left up to the states.”

But any private assurances Sessions may have given Gardner before his confirmation hearing were not necessarily evident in that testimony. He told senators who asked him about this very issue that “one obvious concern is that the United States Congress has made the possession of marijuana in every state and distribution of it, an illegal act.”

He went on to suggest that it fell to Congress to change the classification of marijuana as an illegal drug if it didn’t want DOJ to enforce the law against it. 

“It’s not so much the attorney general’s job to decide what laws to enforce,” Sessions said. “We should do our job and enforce laws effectively as we’re able.”

Sessons’ anticipated action would be a departure from the Obama administration’s policy, which issued guidance in 2013 that it would not interfere in state and local initiatives to legalize marijuana, as long as they didn’t interfere with federal law enforcement priorities.

In an interview with Rolling Stone just after he left office, Obama explained the dilemma for the Justice Department in prosecuting the federal ban on pot, which is considered a Schedule 1 drug, one which the FDA says has no medical use and has a high potential for abuse.

“[I]t is untenable over the long term for the Justice Department or the DEA to be enforcing a patchwork of laws, where something that’s legal in one state could get you a 20-year prison sentence in another,” Obama told Rolling Stone. “There’s something to this whole states-being-laboratories-of-democracy and an evolutionary approach. You now have about a fifth of the country where this is legal.”

Sessions, however, compares marijuana to heroin and blames it for spikes in violence.

CBS News’ Alan He contributed to this report.

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