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Sixteen social media stars including Zoella, Ellie Goulding and Rita Ora have agreed t change how they post online.

They will have to make it clear on their posts that they have been paid or received any gifts or loans for products they use for advertising purposes

It's after a warning from the people who police adverts - the Competition and Markets Authority (CMA) suggested that their posts could break some laws.

Online ads have been proven to make celebrities and influencers a lot of money and sometimes it's hard to tell what is and isn't an advert.

News organisations have reported that celebrities like Kylie Jenner can make more than £750,000 per post on social media.

The CMA has not said whether the influencers named have broken the law, but said they volunteered to change their practices after an investigation.

They also said that their investigation is ongoing.

Andrea Coscelli, chief executive of the CMA, said: "Influencers can have a huge impact on what their fans decide to buy. People could, quite rightly, feel misled if what they thought was a recommendation from someone they admired turns out to be a marketing ploy.

"You should be able to tell as soon as you look at a post if there is some form of payment or reward involved, so you can decide whether something is really worth spending your hard-earned money on."

Some celebrities do use hashtags such as #ad or #sponsored to indicate that they have been paid to post content.