The Food and Drug Administration and Federal Trade Commission are warning some makers of e-cigarette juices about how they advertise on social media.
Regulators say four companies were issued warning letters because social media posts on their behalf did not include the necessary warnings for nicotine.
Recently, how e-cig companies market their products has come under scrutiny.
Several health and anti-tobacco organizations have asked for federal officials to act on the social media campaigns.
It followed data from the Centers for Disease Control that found over 3.6 million middle and high school students were using e-cigarettes.
The research also showed that the number of young users and how much they used the products were on the rise.