Vape brand Juul is reportedly at the center of a criminal probe

Although it's not clear yet what the crime is.

E-cigarette maker Juul is in trouble again. According to The Wall Street Journal, people familiar with the matter say that the company is the subject of a criminal investigation by federal prosecutors in California. It's not yet been revealed what the focus of the investigation is, although sources say it's still in its early stages.

This will be another unwelcome challenge for the quickly-growing company, which has come under fire for the ways its sleek vaporizers have found appeal with young people. The Federal Trade Commission, Food and Drug Administration (FDA) and several other state attorney generals are already investigating the company's marketing practices, although Juul maintains it never targeted underage users.

Meanwhile, the FDA has opened a wider criminal investigation into vaping in general, following hundreds of reports of vaping-related lung illnesses. This most recent probe may well be moot, though, since the Trump administration has announced plans to ban most flavored e-cigarettes. How that, and this new investigation, will affect Juul remains to be seen.

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