Juul brand vaping pens are seen for sale in a shop in Manhattan in New York City, New York, U.S., February 6, 2019.Mike Segar | ReutersFederal prosecutors in California are conducting a criminal probe into e-cigarette maker Juul, the Wall Street Journal reported Monday.The probe, by the U.S. attorney’s office of the Northern District of California, is in the early stages, the Journal reported, citing people familiar with the matter. The Journal said it was unable to learn the focus on the probe.A spokesperson for Juul and the Northern District of California’s AG office were not immediately available for comment.Regulators have criticized Juul for fueling a teen vaping “epidemic,” scrutinizing the company’s early advertising campaigns that used young models and bright colors health officials say appealed to kids. Critics say the images positioned Juul as a lifestyle brand and attracted young people. Lawmakers have also urged the FDA to pull most e-cigarettes off the market, including market leader Juul, amid an outbreak of a deadly lung disease linked to vaping that has sickened at least 530 people and killed eight.In August, the Journal reported the Federal Trade Commission was investigating whether Juul used deceptive marketing and targeted minors.In 2016, more than 2 million U.S. middle and high school students used e-cigarettes over a 30 day period, according to the Centers for Disease Control and Prevention. The CDC cautions that nicotine exposure can harm adolescents’ brain development.Read the full Wall Street Journal report here.—CNBC’s Angelica LaVito contributed to this report.This is a developing story. Please check back for updates.