The US Food and Drug Administration is cracking down on electronic cigarette use among teens. The agency announced a new, five-point initiative this week that it says should stop vape companies from marketing to teens and prevent retailers from selling to underage kids. It’s also investigating Juul, the company that’s become synonymous with the cool teens vaping image.

As part of its crackdown, the FDA has been carrying out an undercover operation to identify retailers selling e-cigarettes to young people. So far, it’s issued 40 warning letters to stores around the country, including several 7-Elevens and Shell locations. eBay took down listings of the Juul that apparently could have been sold to kids.

The agency has also asked for information from Juul to help it understand the company’s youth demographic. It’s requested marketing documents, as well as research on the effects of its products. The FDA also admits that it has no idea why teens love the Juul, and it’s hoping the company can help it figure that out through its gathered data. The agency seems to suggest that Juul is well aware that teens use its products and that it might know how to cater to them.

Juul has issued a statement on its website about the investigation and has also launched a “comprehensive strategy to combat underage use.” CEO Kevin Burns writes, “I’m not only a Juul employee, but more importantly I am a parent of teenagers. I never want my 18-year-old-son or 15-year-old daughter to try Juul. The product was designed with adult smokers in mind and their need to break the grip of cigarette dependency.”

Finally, the FDA promises to plan “additional enforcement actions” for companies who market to kids and to continue to educate kids about tobacco products.

The FDA seems especially concerned over the use of nicotine in these products, which makes them addicting, regardless of the age of the user. All Juul pods include nicotine, although the company says on its FAQ page that it’s “constantly working on new developments.” Studies have found that teens who vape are more likely to continue smoking. As of 2016, more than 2 million middle and high school students vaped.