WASHINGTON (AP) — President Donald Trump said Wednesday his administration will propose banning thousands of flavors used in e-cigarettes to combat a recent surge in underage vaping .

The Food and Drug Administration will develop guidelines to remove from the market all e-cigarette flavors except tobacco, Health and Human Services Secretary Alex Azar told reporters during an Oval Office appearance with the president, first lady Melania Trump and the acting FDA commissioner, Ned Sharpless.

Trump said vaping has become such a problem that he wants parents to be aware of what’s happening. “People are going to watch what we’re saying and parents are going to be a lot tougher with respect to their children,” he said.

Melania Trump recently tweeted her concerns over the combination of children and vaping.

It will take several weeks to develop the proposed flavor restrictions, which will be subject to public input before taking effect.

Trump’s first public comments on vaping come as health authorities investigate hundreds of breathing illnesses reported in people who have used e-cigarettes and other vaping devices.

No single device, ingredient or additive has been identified, though many cases involve marijuana vaping devices.

The proposal announced by Trump officials would only apply to nicotine vaping products, which are regulated by the FDA.

The FDA has had the authority to ban vaping flavors since 2016, but has previously resisted calls to take that step. Agency officials instead said they were studying if flavors could help smokers quit traditional cigarettes.

But parents, politicians and health advocates have increasingly called for a crackdown on flavors , arguing that they are overwhelmingly to blame for a recent surge in underage vaping by U.S. teens, particularly with small, discrete devices such as Juul’s.

Anti-tobacco groups praised the announcement but said restrictions must be “immediate.”

“It has taken far too long to stop Juul and other e-cigarettes companies from targeting our nation’s kids with sweet-flavored, nicotine-loaded products,” said Matthew Myers, of the Campaign for Tobacco-Free Kids, in a statement.

A ban on flavors would be a huge blow to companies such as San Francisco-based Juul, which has grown into a multibillion-dollar business by selling mint, fruit and dessert flavored-nicotine products.

Juul and other manufacturers argue that their products are intended to help adult smokers wean themselves off traditional paper-and-tobacco cigarettes. But there is little evidence that e-cigarettes are effective for helping smokers quit.

Representatives for Juul did not immediately respond to a request for comment Wednesday.

A 2009 law banned all flavors from traditional cigarettes except menthol. But that law did not apply to e-cigarettes, which were then a tiny segment of the tobacco market.

“We simply have to remove these attractive flavored products from the marketplace until they can secure FDA approval, if they can,” Azar said.

Azar said flavored products could apply for FDA permission to reenter the market. But under agency standards, only products that represent a net benefit to the nation’s public health can win FDA clearance.

Azar said the administration would allow tobacco-flavored e-cigarettes to remain available as an option for adult smokers. But he said that if children begin using those products, “we will take enforcement action there also.”

Significantly, the Trump proposal is expected to bar menthol and mint vaping flavors. FDA officials have previously exempted those products from any sales restrictions because they were thought to be useful to adult smokers. Anti-vaping advocates criticized that decision, pointing to survey data showing roughly half of teens who vape use mint and menthol.

“Finally, the FDA is doing its job,” said Sen. Dick Durbin, D-Ill., who has prodded the agency for months to take action on flavors.

Scott Gottlieb, who stepped down as FDA commissioner in April, said in a tweet that Juul bore particular responsibility for forcing the administration’s action.

“Unfortunately the entire category of e-cigs was put at risk largely as a result of the youth abuse of mostly one manufacturer’s products,” Gottlieb said.

Wednesday’s announcement came despite months of aggressive lobbying by Juul, which spent $1.9 million in the first half of the year to try and sway the White House, Congress and the FDA.

Several former White House officials, including communications aide Josh Raffel, and Johnny DeStefano, who served as counselor to Trump, have gone on to work for Juul.

Federal law prohibits e-cigarette and all other tobacco sales to those under 18. But last year, 1 in 5 high school students reported vaping in the past month, according to government survey figures. Federal health officials have called the trend an “epidemic,” and new statistics due out this fall are expected to show the problem worsening.

More than 80 percent of underage teens who use e-cigarettes say they picked their product because it “comes in flavors that I like,” according to government surveys.

A few local governments, including San Francisco, have passed bans on flavored tobacco. And this month Michigan moved to become the first state to ban flavored electronic cigarettes. But other proposed flavor bans have stalled in state legislatures this year.

E-cigarettes have been on the U.S. market for more than a decade. FDA officials have repeatedly delayed enforcing regulations on them, responding to industry complaints that it would wipe out thousands of small vaping companies.

Most experts agree the aerosol from e-cigarettes is less harmful than cigarette smoke since it doesn’t contain most of the cancer-causing byproducts of burning tobacco. E-cigarettes generally heat liquid containing nicotine. But there is virtually no research on the long-term effects of vaping.

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Associated Press writer Darlene Superville contributed to this report.