The Food and Drug Administration (FDA) seized more than a thousand documents from e-cigarette maker Juul Labs last week in a surprise inspection, according to The New York Times. The agency said the documents were related to Juul’s sales and marketing practices.

Juul controls 72 percent of the U.S. e-cigarette market, the article notes. The FDA said it wants to find out whether Juul deliberately targeted minors as consumers.

A study published Tuesday in the journal JAMA found Juul Labs’ sales roles from 2.2 million devices in 2016 to 16.2 million last year. Those figures come from retail stores and do not include online sales.

About 3 million—or 20 percent—of high school students are vaping, according to preliminary data from the latest National Youth Tobacco Survey. In contrast, last year 1.73 million—or 11.7 percent—used e-cigarettes.