The UK Advertising Standards Authority (ASA) has ruled that video bloggers, known as "vloggers", must make it clearer when they are promoting products.
The decision followed an investigation by the BBC Newsround, which focused on a group of vloggers who had been paid to promote Oreo biscuits.
The ASA was told that biscuit company Mondelēz had paid a host of YouTube stars to promote its product by filming themselves partaking in an "Oreo lick race."
Among them were Phil Lester and Dan Howell, whose AmazingPhil YouTube channel has more than two million followers.
Lynsay Tafe, of the ASA, said the promotion wasn't clear and stressed that vloggers must now go to greater lengths to signal promotions.
"The brands and the vloggers now have to make it very clear before you click on a video that it is a promotional video," she said.
"Vloggers often have huge followings built on authenticity, built on them providing interesting, funny, natural content.
"We think it's only fair that when they start promoting stuff on behalf of a brand - which is absolutely fine for them to do - that they do so in a way that's clear and upfront with their audience."
But Dr Jonathon Hutchinson, of The University of Sydney, said Australia was yet to catch up.
"In Australian context, there’s no regulation," he said.
"The people who are making the laws, they’re not really focusing on this space just yet, it's kind of a grey area. It's definitely emerging."
