White House press secretary Sean Spicer calls on a reporter during the daily news briefing at the White House in Washington, Thursday, Feb. 9, 2017. Spicer discussed the comments made by Supreme Court Justice nominee Neil Gorsuch and other topics. AP Photo/Carolyn Kaster

Sean Spicer, President Donald Trump's press secretary, warned the burgeoning US marijuana industry that there will be "greater enforcement" of federal laws.

"I think that's a question for the Department of Justice — I do believe that you'll see greater enforcement of it [marijuana]," Spicer said during Thursday briefing, responding to a question regarding the state-federal conflict of marijuana laws.

Marijuana — both recreational and medical — is legal in a number of states, though it's illegal at the federal level, creating a conflict between state and federal regulations.

Jeff Sessions, the attorney general, has been a vocal opponent of legal marijuana in the past.

However, Rep. Dana Rohrabacher (R-CA) introduced a marijuana legalization bill that would resolve state-federal conflicts earlier this month, that frames the issue around state's rights, a common rallying cry for Republicans.

"There's a big difference between medical use... and recreational use, which is something the Department of Justice will be further looking into," Spicer said.

Spicer further said that the federal policy towards medical marijuana is "very different" than for state-legal recreational marijuana.

Spicer brought up a 2014 congressional appropriations rider that specifically forbids the Justice Department from interfering with state-legal medical marijuana. The provision — the Rohrabacher-Farr Amendment — prevents the federal government from cracking down on state-regulated medical marijuana businesses.

The Justice Department was forced to drop a case prosecuting a medical marijuana dispensary in California based on the guidelines stipulated by the Rohrabacher-Farr Amendment last year.

A demonstrator waves a flag with marijuana leaves on it during a protest calling for the legalization of marijuana, outside of the White House in Washington. Jose Luis Magana/AP

Mark Kleiman, a professor of public policy at New York University, told Business Insider in February that while the Justice Department could "destroy the legal market overnight," it would create a "mess," and would be replaced by an "illegal market."

"If a state doesn’t want to enforce its cannabis laws, the Federal government really cannot step into those shoes," Kleiman said.

Spicer further made a dubious connection between recreational marijuana and the opioid addiction crisis that's "blossoming" in a number of states.

"The last thing we should be doing is encouraging people," Spicer said. "There's still a federal law that we need to abide by when it comes to recreational marijuana and other drugs of that nature."

Some research even suggests that medical marijuana could actually reduce demand for opioid-based pankillers.

Spicer, however, clarified that Trump understands the "pain and suffering," that many people facing terminal diseases go through, and the "comfort" that drugs like medical marijuana can provide patients.

Trump himself indicated on the campaign trail that he'll consider recreational marijuana a "state's rights," issue, but his Administration has not outlined an offical position on the issue.

Fighting recreational marijuana may prove to be an unpopular move. A Quinnipiac University poll released on Thursday indicates that 59% of voters think marijuana should be legalized, with 76% of 18-34 year-olds in favor of legalization.

And, perhaps the issue with the most bipartisan support — 93% of voters support allowing doctors to prescribe medical marijuana.