(CNN)- The FDA is expanding its investigation into e-cigarettes.
The agency is now targeting 21 e-cigarette companies to find out if they been marketing products illegally.
The move comes less than two weeks after the FDA conducted a surprise inspection of e-cigarette maker Juul's Corporate Headquarters in San Francisco.
Agents seized thousands of documents, many relating to sales and marketing.
The investigations are part of the FDA’s crack-down on teen e-cigarette use.
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