Communities are steeling for a “states’ rights” battle over the cultivation and sale of recreational marijuana after the federal government’s warning about a crackdown last week.

“There’s still a federal law that we need to abide by when it comes to recreational marijuana,” White House Press Secretary Sean Spicer said last Thursday. “Recreational use ... is something the Department of Justice will be looking into,” he added, saying he believes “you’ll see greater enforcement” of federal law.

Pot remains illegal under the federal Controlled Substances Act, even though recreational use of marijuana has been approved in eight states and Washington, D.C. It’s legal for medical use in 28 states and the nation’s capital.

Now growers, users and even state officials are preparing for a fight. A major concern is revenue. The nonprofit Tax Foundation estimates that a mature legalized marijuana industry would generate up to $28 billion in tax revenue for federal, state and local governments. Colorado raked in $70 million in taxes in 2015, exceeding expectations.

The legal marijuana industry in the U.S. could create more than 250,000 jobs by the year 2020, according to a New Frontier Data report. That’s more than the projected job gains in the manufacturing industry, according to the Bureau of Labor Statistics.

States Push Back

In Washington state, which legalized recreational use of the drug with Colorado in 2012, state Attorney General Bob Ferguson vowed to defy a federal crackdown.

“I will resist any efforts by the Trump administration to undermine the will of the voters in Washington state,” Ferguson told The Seattle Times.

In a Feb. 15 letter to U.S. Attorney Jeff Sessions, Ferguson and Washington Gov. Jay Inslee (D) outlined the arguments for keeping pot legal in the state, including the fact that the legal marijuana industry is expected to generate a whopping $272 million in taxes in financial year 2017.

A federal crackdown would only force the industry “back underground, returning bumper profits to criminal groups while once again depleting government resources,” the letter adds.

Colorado Gov. John Hickenlooper (D) had opposed legalizing marijuana until voters approved it in his state, but it’s “now part of our [state] Constitution,” he said on NBC’s “Meet The Press” on Sunday.

“Over 60 percent of American people are now in a state where either medical or recreational marijuana is legalized. It’s become one of the great social experiments of our time,” he said.

“I think it’s the wrong time to pull back from this experiment, and if the federal government’s going to come and begin closing in and arresting people that are doing what’s legal in different states, my God, it creates a level of conflict that’s going to be very difficult,” Hickenlooper told MSNBC on Friday.

If Trump orders pot raids, @GovOfCO: "oh my God, it creates a level of conflict that's going to be very difficult." https://t.co/2TJ657SKpO — Jacob Soboroff (@jacobsoboroff) February 24, 2017

California Lt. Gov. Gavin Newsom, also a Democrat, fired off a letter to President Donald Trump on Friday, urging him to “work in partnership with California and the other … states that have legalized recreational marijuana for adult use.”

The government “must not strip the legal and publicly-supported industry of its business, and hand it back to drug cartels and criminals,” Newsom added.

California legalized recreational use of marijuana in November. State officials formulating specific pot regulations are proceeding with plans to license growers and sellers, despite Spicer’s warning, they said last week.

“Until we see any sort of formal plan from the federal government, it’s full speed ahead for us,” Alex Traverso, a spokesman for the California Bureau of Medical Cannabis Regulation, told the Los Angeles Times.

Bipartisan Cooperation

Rep. Dana Rohrabacher (R-Calif.) has introduced a bill called “Respect State Marijuana Laws” that would block enforcement of federal laws against local operations that comply with state regulations on legalized pot. It has been co-sponsored by 14 members of Congress.

Rohrabacher is part of a new, Congressional Cannabis Caucus that also includes Reps. Don Young (R-Alaska) and Earl Blumenauer (D-Ore.) and Jared Polis (D-Colo.), Fortune reports.

Sen. Ron Wyden (D-Ore.) has also called on the federal government to “respect the decisions of Oregon voters.”

“The Trump Administration is threatening states’ rights, including the rights of one in five Americans who live in a state where marijuana is legal,” Wyden said. “I will fight hard against ridiculous federal government intrusions into our state.”

Recreational growers and users could switch horses for a time and move into the medical marijuana field, which doesn’t seem high on the administration’s list of priorities ― or they’ll simply go underground.

‘I Think It’s Up To The States’

During the presidential campaign, Trump said marijuana laws should be left up to the states. In a 2016 interview about legal recreational marijuana in Colorado, he said, “I think it’s up to the states, yeah. I’m a states person. I think it should be up to the states, absolutely.”

But marijuana supporters are concerned that he’s changing his tune, in part because of Sessions’ antipathy toward the drug. Sessions said in April that “good people don’t smoke marijuana.”

Spicer came under fire for linking marijuana use to opioid addictions. “You see the opioid addiction crisis blossoming; the last thing we should be doing is encouraging people [through legal marijuana],” he said Thursday.

Yet a 2017 analysis of research by the National Academy of Sciences found little evidence that marijuana use is linked to opioid addictions. Studies have shown that opioid overdose death rates are lower in states that have legalized medical marijuana. Some medical experts even believe that marijuana could be used to help addicts wean themselves from opioids.

CORRECTION: A previous version of this article misstated that medical marijuana is legal in 30 states. It’s legal in 28, plus Washington, D.C.