The Justice Department may step up enforcement of federal marijuana laws in states that have voted to legalize its recreational use, according to White House press secretary Sean Spicer.

"I do believe you'll see greater enforcement of it," Spicer said, during his daily press briefing. He added that the Department of Justice will be looking into the issue further.

Spicer's comments offer an indication of how the Trump administration may approach the nation's fast-growing cannabis industry. New Attorney General Jeff Sessions has been less direct when asked about marijuana, saying during his confirmation hearings that he would "review and evaluate" existing policies.

Roughly one in five Americans now live in a state where non-medical marijuana is legal for adults, and that number may be growing. Lawmakers in Maryland have recently proposed bills allowing recreational use. Medical use of cannabis is allowed in 28 states and the District of Columbia.

Spicer differentiated between medical and recreational use of the plant, saying President Trump "understands the pain and suffering that many people go through who are facing especially terminal diseases and the comfort that some of these drugs, including medical marijuana, can bring them."

Recreational marijuana, he said, is a "very, very different subject."

The majority of Americans support marijuana legalization, according to a new poll by Quinnipiac University. It also found that 71 percent of voters believe the government should not enforce federal laws against marijuana in states that have legalized it.

"The vast majority of Americans agree that the federal government has no business interfering in state marijuana laws," said Mason Tvert, the communications director for the Marijuana Policy Project, in a statement. "This administration is claiming that it values states' rights, so we hope they will respect the rights of states to determine their own marijuana policies."

There has been a growing uncertainty in the multibillion-dollar marijuana industry about how the Trump administration would approach enforcement of federal drug laws.

Regulated marijuana sales totaled $6.7 billion in 2016, according to Arcview Market Research, and it's projected to grow to an estimated $20.2 billion by 2021. But marijuana is still illegal under federal law. The industry has been growing under the auspices of the so-called Cole Memo, put in place by the Obama administration in 2013. That memo said federal prosecutors would not intervene in states' marijuana laws as long as cannabis didn't cross state lines and the states followed a set of guidelines.

There's been concern since the election that Trump could move to undo that memo. As a candidate, Trump said that recreational marijuana should be a state issue. Attorney General Sessions said as early as last year that "good people don't smoke pot."

Washington state's attorney general, Bob Ferguson, who led the lawsuit against Trump's travel ban, has already said that he would oppose any moves by the administration to interfere with his state's marijuana laws. In a letter to Sessions, he wrote: "My office will use every tool at our disposal to ensure that the federal government does not undermine Washington's successful, unified system for regulation recreational and medical marijuana."

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