Attorney General Jeff Sessions on Thursday rescinded an Obama-era policy that had paved the way for a flourishing legalized marijuana industry, triggering a resounding backlash from Oregon's top elected officials while sending shockwaves through the state's cannabis marketplace.

The U.S. Justice Department rollback, outlined in a three-paragraph memo by Sessions, a longstanding marijuana foe, will let federal prosecutors decide how aggressively to enforce federal marijuana law in states where pot is legal.

In Oregon that authority rests with Billy J. Williams, who as the state's U.S. attorney has the power to crack down on the production, distribution and use of marijuana.

Williams, nominated in November by President Donald Trump to remain in the job, indicated that his office would target the state's illicit marijuana operations -- which are thriving, according to state and federal law enforcement authorities.

"We will continue working with our federal, state, local and tribal law enforcement partners to pursue shared public safety objectives, with an emphasis on stemming the overproduction of marijuana and the diversion of marijuana out of state, dismantling criminal organizations and thwarting violent crime in our communities," he said in a statement.

Williams didn't return calls for further comment.

Oregon State Police Superintendent Travis Hampton said: "We will not target people operating lawfully within state statute."

The Sessions edict will likely add to confusion about the recreational marijuana programs in Oregon and other states because long-standing federal law prohibits them. Stock prices for a number of publicly traded marijuana companies plunged shortly after the announcement.

The move comes days after retail pot shops opened for business in California, creating what industry analysts say will become the world's largest market for legal marijuana. In Oregon, recreational cannabis has helped generate thousands of jobs and pumped millions of dollars into state coffers.

Since 2012, eight states and Washington, D.C., have voted to legalize the recreational use of marijuana. A total of 28 states have legalized pot for medical purposes.

A recent Gallup poll found that 64 percent of Americans now support the legalization of marijuana, a record high.

"We've had steady progress for five years now, building momentum," said U.S. Rep. Earl Blumenauer, D-Portland, who heads the Congressional Cannabis Caucus.

"Mr. Sessions is out of touch with that, and I think that it's important for people who support this reform to renew their efforts because it's making a difference in states around the country."

A slew of other Oregon politicians, including Gov. Kate Brown and U.S. Sens. Ron Wyden and Jeff Merkley, all Democrats, fired off terse statements that condemned Sessions' decision while defending the state's marijuana industry.

Oregon was the first state to decriminalize personal possession of marijuana in 1973 and legalized medical marijuana in 1998. Voters overwhelmingly approved its recreational program in 2014, becoming the third state behind Colorado and Washington to do so.

"This is an industry that Oregonians have chosen -- and one I will do everything within my legal authority to protect," Oregon Attorney General Ellen Rosenblum said in a statement.

Despite marijuana remaining a Schedule 1 drug -- alongside the likes heroin and LSD -- the Justice Department under President Barack Obama moved to keep federal prosecutors from interfering in states' legal pot activity.

That mandate, outlined in an opinion called the Cole memo, helped pave the way for legal marijuana initiatives like Oregon's -- and gave birth to what's now a multibillion-dollar industry across the U.S.

Oregon's legal marijuana market employed more than 20,000 people last year and generated close to $450 million in sales, said Beau Whitney, a senior economist with New Frontier Data, a market research firm.

Data compiled by the Oregon Department of Revenue shows that the state collected more than $70 million in taxes from the sale of pot last year, which help fund education, law enforcement and other public services.

In his decision, Sessions rescinded the Cole memo along with three other guidelines for marijuana enforcement outlined by Obama's Justice Department.

"The previous issuance of guidance undermines the rule of law and the ability of our local, state, tribal, and federal law enforcement partners to carry out this mission," Sessions wrote.

The news stunned people in Oregon's cannabis industry.

Amy Margolis, a Portland attorney who advises cannabis businesses, said she woke up to texts and emails from clients worried about the implications of the new approach.

She said legal marijuana business owners understand they're violating federal law by getting into the industry, but they've felt the Cole memo offered protection from prosecution.

"The Cole memorandum really, truly provided some comfort that to those who were compliant and legal and following state laws, that they would be safe," she said. "Right now at this moment we don't know how true that will remain."

She said the move is likely to chill efforts in other states to legalize marijuana and will almost certainly discourage investors.

"It's certainly one of the worst things that the attorney general could have done to the cannabis industry," she said.

A staunch conservative from the deep South, Sessions has been a vocal opponent of marijuana legalization for much of his public life. "Good people don't smoke marijuana," the 71-year-old said during a Senate hearing in 2016.

"We need grown-ups in Washington to say marijuana is not the kind of thing that ought to be legalized, it ought not to be minimized, that it is in fact a very real danger."

Since becoming attorney general last year, he has assailed marijuana as comparable to heroin and blamed it for spikes in violence.

As for Trump's personal views on marijuana? They remain largely unknown.

Even as Trump ran for president on a law-and-order platform he appeared to show little interest in meddling much in states that allow medical or recreational use of marijuana.

"In terms of marijuana and legalization, I think that should be a state issue, state-by-state," Trump said during a political rally in October 2015.

Regardless, the decision was a win for pot opponents who had been urging Sessions to take action.

"The days of safe harbor for multimillion-dollar pot investments are over," said Kevin Sabet, president and CEO of Smart Approaches to Marijuana, an anti-marijuana advocacy group. "This is a good day for public health."

The Associated Press and Oregonian/OregonLive reporters Noelle Crombie and Jim Ryan contributed

-- Shane Dixon Kavanaugh

skavanaugh@oregonian.com

503-294-7632 || @shanedkavanaugh.