The Food and Drug Administration conducted a surprise inspection at the offices of Juul Labs—a large e-cigarette maker—last week and walked away with more than a thousand pages of documents related to the company’s marketing and sales practices, The New York Times reported.

Juul, which controls 72 percent of the e-cigarette market, has recently come under fire for allegedly marketing its products to underage teenagers, and its products have become widely popular in U.S. high schools.

“The new and highly disturbing data we have on youth use demonstrates plainly that e-cigarettes are creating an epidemic of regular nicotine use among teens,” the FDA said in a statement. “It is vital that we take action to understand and address the particular appeal of, and ease of access to, these products among kids.”

The raid marks a significant ramp up in pressure on the e-cigarette market as concerns mount over the rapid increase of vaping among youths. About 3 million high school students said they used e-cigarettes within the last 30 days, a jump of 75 percent since last year, according to one recent study. Teenagers who start vaping, or using e-cigarettes, are more likely to smoke traditional cigarettes, other studies show.

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