WASHINGTON (Reuters) - Four dominant e-cigarette manufacturers face a probe into the health impacts of their products, as the U.S. House Energy and Commerce Committee asked on Wednesday about the firms’ research and marketing practices.

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The committee sent letters to Juul Labs Inc, 35% owned by Marlboro maker Altria Group Inc, Fontem Ventures, Japan Tobacco Inc, and Reynolds American Inc, a unit of British American Tobacco Plc.

The letter to Juul asked if the company has conducted or financed studies on the health implications of using its products and the effectiveness of Juul in helping users quit smoking. It asked if Juul has sent information to the Food and Drug Administration.

Kaelan Hollon, a spokeswoman for Reynolds American, said the company is reviewing the letter and believes “minors should never use tobacco products, including vapor products.”

Japan Tobacco said in a statement it welcomes any opportunity to “set out the responsible approaches” it takes in its marketing.

Juul and Fontem Ventures did not respond to requests for comment.

The probe comes amid growing scrutiny of the e-cigarette industry by lawmakers. A separate House panel in July released internal Juul emails that committee staff described as attempts to “enter schools and convey its messaging directly to teenage children.”

James Monsees, Juul’s co-founder and chief product officer, told the panel the company’s target audience is adult cigarette smokers.

Representative Frank Pallone, the Democratic chair of the committee, cited vaping-related lung illnesses recently reported by the Centers for Disease Control and Prevention. He requested answers and documents by Sept. 20.

The CDC said on Wednesday it is investigating 153 possible cases of severe lung illness associated with e-cigarette use in 16 states. No deaths have been reported, they said.