Long lines greeted the opening of legal marijuana retail stores in Southern California.
Robert Hanashiro, USA TODAY

WASHINGTON – As part of a crackdown on legal marijuana, the Justice Department is set to roll back an Obama administration policy to not challenge state laws that allow people to use pot for medical and recreational uses an official familiar with matter said Thursday.

The move represents a dramatic shift in marijuana enforcement policy. The official, who is not authorized to comment publicly ahead of a formal announcement, said details of the new policy to reverse a 2013 Obama administration directive of non-interference would be outlined later Thursday.

Attorney General Jeff Sessions has long signaled his disagreement with the previous administration’s stance on pot, which did not challenge state laws, as long as marijuana sales did not conflict with federal law enforcement policies.

The Obama policy, which represented a major breakthrough by advocates for the decriminalization of marijuana use, did not change marijuana’s classification as an illegal drug. But it effectively discouraged the pursuit of non-violent marijuana users who have no links to criminal gangs or cartel operations.

The expected move injected fresh uncertainty into an industry that has flourished largely because federal prosecutors have maintained their hands-off approach.

Sessions’ decision to revoke the previous administration policy should be a warning sign to institutional investors, said Kevin Sabet, director of the anti-legalization group Smart Approaches to Marijuana and a former federal drug-control expert who served in the Clinton, Bush and Obama administrations. 

“It signals the end of safe harbor for major pot investors,” Sabet said. “This throws up everything in the air one thought they knew about the federal government‘s position on marijuana, which up to this date was more of a ‘see no evil, hear no evil’ policy.”

The announcement comes the same week California launched recreational marijuana sales for adults. Every state that’s approved recreational pot sales – Alaska,…