• by Wendy Davis  @wendyndavis, September 15, 2017

Actress Lindsay Lohan, model Naomi Campbell and reality TV star Nicole "Snooki" Polizzi were among the 21 Instagram influencers to recently receive warning letters from the Federal Trade Commission.

The letters, dated Sept. 6, were sent by the FTC to 21 of the 47 celebrities who previously received official reminders about their obligation to disclose paid endorsements. The agency disclosed the names of recipients in response to a Freedom of Information Act request by Reuters.

The FTC's letters to the celebrities provided examples of potentially problematic Instagram posts. For instance, Lindsay Lohan allegedly posted a video of herself on Instagram and wrote, "Cooking on a #boat In @alexanderwangny."

"The FTC staff believes that tagging a brand or business is an endorsement of the brand or business," the letter to Lohan states. "Accordingly, if you have a material connection with a tagged business or the marketer of a tagged brand, then your posts should disclose that connection."

Advocacy group Public Citizen, which recently urged the FTC to crack down on undisclosed Instagram ads, says the warning letters don't go far enough to protect consumers.

“Undisclosed paid posts on Instagram for products like alcohol, cosmetics and clothing have become a regular part of using the platform, which is dominated by young and impressionable users," Public Citizen stated.

The group is calling for the FTC to prosecute companies that arrange for influencer marketing, or influencers who don't disclose their ties to the companies they promote on social media.