Solace Vapor, Hype City Vapors LLC, Humble Juice Co. LLC and Artist Liquid Labs each received a letter. They now have 15 days to review their marketing, including posts on social media, and to make the necessary disclosures. "These letters are a reminder that companies who use social media influencers to promote their products must comply with all applicable advertising requirements," said Andrew Smith, Director of the FTC's Bureau of Consumer Protection. "Moreover, ads must disclose material health or safety risks—in this case, the fact that nicotine is highly addictive."

This isn't the first time the FTC has issued warnings to social media's stars. It's already warned that paid posts should include terms like ad, promotional or sponsor. Tagging #sp or #partner isn't enough. Even Instagram and YouTube's built-in notification tools that label sponsored content may be too subtle for the FTC. And earlier this year, the FDA expressed concern that vaping companies Juul and Altria might be undermining efforts to prevent use by teens. While vaping and social media influencers are relatively new phenomena, the same old rules apply.