Dozens of celebrities have been warned about endorsing products on social media without declaring they had been paid to do so, the government has said.
The Competition and Markets Authority (CMA) also warned the firms paying them and forced the intermediary, Social Chain, to undertake to stop.
But the CMA insisted on keeping the names of the public figures and the companies secret.
Transparency campaigners said the names should be released
A CMA investigation found that Social Chain arranged for “widely followed social media personalities” to promote films, games, takeaway and dating apps, without declaring that the content was paid-for advertising. They posted the adverts on Twitter, YouTube and Instagram, the government body said.
It added that Social Chain organised 19 marketing campaigns featuring undisclosed advertising in a four-month period last year.
The posts appeared on social media accounts with a “combined reach of around four million followers” and some of the campaigns “trended on Twitter, which may have increased their readership further”.