The Food and Drug Administration announced Friday it will investigate whether more than 40 vaping products are being illegally marketed.

“Companies are on notice – the FDA will not allow the proliferation of e-cigarettes or other tobacco products potentially being marketed illegally and outside of the agency’s compliance policy, and we will take swift action when companies are skirting the law,” FDA Commissioner Scott Gottlieb said in a statement, adding that the increased crackdown stems from kids’ increased use of vapor products.

The FDA sent letters to the 21 e-cigarette companies that could be going against FDA compliance, and asked for information about 40 products that could be in violation.

As part of a plan on tobacco and nicotine regulation, the FDA implemented a new compliance policy that extended the deadline for vapor product manufacturers to submit applications for its products.

The FDA hopes the extension will let manufacturers to explore more meaningful ways to make tobacco products less toxic, appealing and addictive to users.

[Also read: FDA warns company to stop putting erectile dysfunction drugs in e-cigarette liquid]

“These measures, which will focus on protecting youth, could include an examination of flavors/designs that appeal to children, child-resistant packaging and product labeling to prevent accidental child exposure to liquid nicotine,” the FDA said.

Since extending the deadline, the FDA has received complaints that vapor product companies may be marketing new products that do not meet the Food Drug and Cosmetic Act’s requirements. The release said violations could include introduction of new product features, formulations or flavors.

“The FDA remains committed to the potential opportunity for e-cigarettes to help adult smokers transition away from combustible cigarettes. But we cannot allow that opportunity to come at the expense of addicting a whole new generation of kids to nicotine,” Gottlieb said.