Fueling speculation that the Trump administration will try to block California and other states from allowing recreational marijuana use, U.S. Attorney General Jeff Sessions told state attorneys general Tuesday that he was “dubious” about the trend.

“I am dubious about marijuana. … I’m not sure we’re going to be a better, healthier nation if we have marijuana sold at every corner grocery store,” he said in a speech at the winter meeting of the National Association of Attorneys General.

Related: Feds threatening to shut down Las Vegas Cannabis Cup

Even as states vote to legalize recreational pot — with California, Massachusetts, Maine and Nevada voting to do so just last November — the possession and sale of marijuana is still a federal crime, creating a source of tension between the states and the feds.

Sessions has long opposed legalization, calling pot “a real danger” in a Senate hearing last year on the subject. But the former Alabama senator has not clearly said what he plans to do about it, and a cloud of uncertainty hangs over the industry. Tuesday’s comments came one day after he told reporters that there was “more violence around marijuana than one would expect.”

“I think everyone’s just waiting anxiously to see what they have in store,” said Priscilla Vilchis, the Los Angeles-based CEO of Premium Produce, which has cultivation and manufacturing licenses in Nevada and is trying to expand to California.

Last week, White House Press Secretary Sean Spicer suggested the Department of Justice would crack down on recreational marijuana while allowing states to permit certain uses of the drug for medicinal purposes.

“I do believe you’ll see greater enforcement,” Spicer said.

In his speech on Tuesday, Sessions also disputed the notion that marijuana could aid in the treatment of opioid addiction, as some have suggested.

“This is the kind of argument that’s been made out there to just almost a desperate attempt to defend the harmlessness of marijuana or even its benefits,” he said. “I doubt that’s true. Maybe science will prove I’m wrong, but at this point in time, you and I have a responsibility to use our best judgment — that which we’ve learned over a period of years — and speak truth as best we can.”

The attorney general’s comments drew criticism from some in the cannabis industry. “Sessions admits he has no idea if cannabis has any benefits,” said Matt Smith-Caggiano, executive director of the The National Organization for the Reform of Marijuana Laws’ Humboldt County chapter. “He has no truth to speak of other than ignorance and closed mindedness.”

Sessions also said he is reviewing the U.S. Department of Justice’s 2013 memorandum commonly known as the Cole Memo, which provided guidance to federal prosecutors and law enforcement on enforcing marijuana laws for states that have legalized cannabis use and sales.

Chrystal Ortiz, operations manager of the medical cannabis brand True Humboldt, said she hoped the regulations California is developing — to be in line with that guidance — “will protect the medical cannabis market in California and hopefully the adult use market.”

“I am glad he is looking into the Cole memo,” she said.