The Food and Drug Administration plans to explore regulating the level of nicotine in conventional cigarettes, a radical step that would reshape the $130 billion American tobacco industry and potentially encourage millions of people to quit smoking.

The move, announced Friday, would represent one of the most sweeping federal efforts to reduce smoking since Congress required cigarette packages to carry health warnings in 1965. It follows other moves by President Donald Trump’s FDA Commissioner Scott Gottlieb to try to deal with the high cost of prescription drugs and opioid addiction, two issues not directly within the agency’s traditional mandate.

Tobacco stocks plunged after the announcement, which came just hours after the failure of Republicans’ effort in Congress to repeal and replace much of the Affordable Care Act. The FDA’s move is likely to set off a lobbying fight in Washington over the proposal, even as it pushes the industry to move faster in the development of new products that rely less on burning tobacco and more on potentially lower-risk technologies like vaping.

“The overwhelming amount of death and disease attributable to tobacco is caused by addiction to cigarettes — the only legal consumer product that, when used as intended, will kill half of all long-term users,” Gottlieb said in a statement announcing the move. “Unless we change course, 5.6 million young people alive today will die prematurely later in life from tobacco use.”

Gottlieb also said regulators will look at banning menthol and flavored products because of their potential for attracting young people.

In a briefing Friday, he called nicotine both the “problem” and “ultimately, the solution.” Along with nicotine reduction, the FDA plans to ease the path of entry for less-harmful nicotine delivery systems. The FDA “must also recognize potential for innovation to lead to less harmful products,” Gottlieb said.

“I’ve pledged a deep commitment to taking aggressive steps to address the epidemic of addiction to opioids,” he said. “I view our opportunity to confront addiction to nicotine with the same obligation. I’ll pursue efforts to reduce addiction to nicotine with the same vigor.”

While reducing nicotine is bad news for the cigarette business, the impact could be tempered for companies like Philip Morris International and Altria Group, which have been putting more emphasis on innovations they say have less health risks. Philip Morris has spent over $3 billion on developing its reduced-risk portfolio.

Representatives of Philip Morris, Altria and British American Tobacco’s Reynolds American division were not immediately available for comment.