Under the finalized rules, e-cigarette manufacturers will have to seek FDA marketing approval for their products, and sales to minors under the age of 18 will be strictly prohibited. (A few states have permitted sales of e-cigarettes and vaping products to minors.) Under the new FDA rule, vaping and other tobacco products will also have to carry warning labels about nicotine’s addictive properties.

“We have more to do to help protect Americans from the dangers of tobacco and nicotine, especially our youth,” said Department of Health and Human Services (HHS) Secretary Sylvia Burwell in a statement. “As cigarette smoking among those under 18 has fallen, the use of other nicotine products, including e-cigarettes, has taken a drastic leap. All of this is creating a new generation of Americans who are at risk of addiction.”

Critics immediately pounced, tarring the the FDA rule as regulatory overreach that will put many small vape shops out of business. Conducting the studies required for FDA approval can be quite costly, meaning that Big Tobacco e-cigarette makers like Imperial Tobacco (which owns the hugely popular blu e-cigarette brand) and Reynolds American (owner of VUSE e-cigs) would likely gain a significant advantage over smaller manufacturers under the regulations.

“This is going to be a grim day in the history of tobacco-harm reduction,” Greg Conley, president of the American Vaping Association, told the Wall Street Journal. “It will be a day where thousands of small businesses will be contemplating whether they will continue to stay in business and employ people.”

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The FDA regulations do contain a grandfather clause nixing the marketing approval requirements for e-cigarette, hookah tobacco, and other such products which were already available as of February 15, 2007. (In the meantime, Congress also is considering a bill that would expand the grandfather clause, exempting many more e-cig products from having to retroactively chase marketing approval.)

The vaping boom has largely taken place during the past five years, with the current $3.5 billion market growing by triple digits for five consecutive years since 2010 (although there is some evidence that growth rate was slated for a slowdown even before the FDA announced its new regulations).

Public health advocates have been pushing for the FDA to take action, however, noting the alarming jump in e-cig use among teens. About 16% of high school students use e-cigarettes, according to recent CDC data—a significant spike since 2011. The e-cigarette industry has insisted that its products are the lesser evil since they don’t contain all the harmful carcinogens that regular tobacco products do. In fact, manufacturers regularly fall back on the line that vaping actually improves public health and can be used as a smoking cessation product.

The existing evidence is more mixed. In a 2015 report by the Center for Environmental Health, entitled, “Smoking Gun: Cancer-causing chemicals in e-cigarettes,” the group said it found the majority of e-cigarettes and other vaping products tested contained high levels of cancer-causing chemicals formaldehyde and acetaldehye. The group also said it was “concerned about the unregulated marketing of e-cigarettes, and especially sales to teens and young people, while little is known about the health hazards from inhaling e-cigarette smoke.”

Additionally, some studies have shown that young e-cigarette users are also more likely to use conventional tobacco products and be established smokers, suggesting that vaping is not so much a smoking deterrent as it is yet another smoking option for kids.

The FDA has broadly increased its tobacco regulation powers under the Family Smoking Prevention and Tobacco Control Act of 2009. In 2013, it used its new authority to reject several proposed tobacco products for the first time in history (rather than just placing restrictions on advertising).