Tobacco companies need to step up efforts to stop kids from vaping, according to a warning from U.S. Food and Drug Administration Commissioner Scott Gottlieb.

The comments are the latest in a series of FDA efforts to crack down on companies that are producing e-cigarettes and selling them to minors. E-cigs like the products made by Juul Labs Inc. are the newest craze in underage tobacco use as youth smoking rates of combustible cigarettes hover around historic lows.

Tobacco companies shouldn’t build businesses that rely on getting kids hooked on nicotine, Gottlieb said in prepared remarks at the American Society of Clinical Oncology’s annual meeting in Chicago. Instead, companies need to help address the problem.

“They better step up and step up soon – to address these trends along with us,” he said. “So far, I must say, I’ve mostly been disappointed by the tepid response from companies that know that a meaningful portion of their sales are being derived from kids.”

Gottlieb’s campaign against youth vaping is part of an attempt to enact broader tobacco regulations. He proposed in July a two-pronged plan to reduce tobacco-related deaths in the U.S. The first half of the plan is to reduce the amount of nicotine in combustible cigarettes. The second half is to ease the regulatory pathway for products that are less harmful sources of nicotine. If enacted, the rules would comprise the most sweeping tobacco overhaul since 1964.

Vaping may be a good alternative for smokers, but young people are picking up the habit, too. The FDA said it sent warnings to 40 retailers for selling Juul products to kids in April. In May, the agency sent 13 letters to manufacturers of nicotine-containing liquids objecting to branding that resembles juice boxes, candy and cookie packages.