In 2015, Machinima, a California-based online entertainment network, caught the eyes of federal regulators for paying so-called social media “influencers” to promote Microsoft's Xbox One system and several games on YouTube.

In March 2016, regulators turned their attention to the retailer Lord & Taylor, which paid influencers to post photographs of themselves on Instagram sporting a paisley dress from a new fashion line. That summer, it was Warner Bros. Home Entertainment Inc., whose marketing campaign for the video game “Middle Earth: Shadow of Mordor” involved paying influencers to post positive reviews on YouTube and other social media sites.

The Federal Trade Commission in those cases faulted the influencers for failing to disclose the payments behind their seemingly organic endorsements. But the FTC only reached settlements with the companies, raising a question of when—if ever—the agency would directly go after the influencers.