US truth-in-advertising enforcers have written to supermodel Naomi Campbell, actresses Lindsay Lohan and Vanessa Hudgens and other celebrities asking whether they are paid to endorse products on the photo-sharing app Instagram.
The letters sent by the US Federal Trade Commission to 21 people with large Instagram followings represent an escalation of the agency's interest in so-called social media "influencers."
Instagram, which is owned by Facebook Inc, has seen a sharp increase in recent years in promotions of products and services by famous people, often without disclosures of whether there was an endorsement deal.
Celebrities have talked up clothing brands, food, alcohol, spa treatments and a wide array of other items.
The letters demand responses by September 30 on whether the celebrities had any "material connection" to marketers whose wares they promoted on the app.
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Others receiving letters included reality star Nicole "Snooki" Polizzi, "Modern Family" star Sofia Vergara, model Amber Rose and Scott Disick, an ex-boyfriend of reality star Kourtney Kardashian.
No representatives for the celebrities could immediately be reached for comment on Wednesday. The FTC declined to comment.
Reuters obtained copies of the letters after filing a Freedom of Information Act request with the government.
In Campbell's case, the FTC said an Instagram post of hers that showed three suitcases made by Globe-Trotter had "recently come to our attention." The post had no disclosure about compensation, according to the letter.
If Campbell had a marketing deal, then she should tell the FTC what actions she is or will be taking to ensure disclosure, the letter says.
Campbell's Instagram account has 4.3 million followers. Hudgens has the most of the group, at 26.7 million.
