The US Federal Trade Commission has ordered a half-dozen e-cigarette companies to turn over sales and advertising data, the federal regulator said on Thursday, in the first sign of a likely probe into their marketing practices.

The order was sent to JUUL Labs Inc, RJ Reynolds Vapor Company, Fontem US Inc, Logic Technology Development LLC , Nu Mark LLC and NJOY LLC, the FTC said in a statement.

The FTC is seeking annual sales data and information on giveaways, data on product placement and flavors, as well as information on the companies’ use of celebrities as internet influencers and marketing on college campuses to sell the electronic smoking devices. The first order was sent about a month ago, an FTC official said.

Altria Group Inc, which owns Nu Mark and has a 35% stake in Juul, will comply with the FTC request for information on Nu Mark, a company spokesman said. A Juul spokesman said the company will fully cooperate with the FTC.

A Fontem Ventures spokeswoman said the company has been working with the FTC and will meet the request’s deadline. Reynolds American said it is reviewing the request, while Japan Tobacco said it is looking forward to continuing its dialogue with the FTC.

The FTC order comes a week after a US House panel asked Fontem Ventures, Reynolds American, NJOY, and Japan Tobacco (2914.T), which owns Logic, to stop all advertising of their products in the United States. Juul had said the same day that it would pull its ads.

The requests come amid a mysterious outbreak of serious vaping-related lung illnesses whose cause has yet to be determined.

The US Centers for Disease Control and Prevention has said that there have been 805 confirmed and probable cases of lung illness in 46 states, as well as 12 deaths associated with vaping in the United States. Four other US deaths have since been reported by states. The CDC is expected to update its numbers later on Thursday.