Celebrities including Nicole Richie, Kim Kardashian, Whitney Port and Audrina Patridge can reportedly earn up to $10,000 per Tweet for companies including Sony and Nestle.
Alias actor Greg Grunberg who donates his Tweet fees to charity, earns in the four figures per paid Tweet, Ad.ly's CEO Sean Rad tells the Web site.
Who are the ultimate paid Tweeters? According to Rad the most lucrative would be Britney Spears or P. Diddy who could earn up to $20,000 per Tweet.
So, how can fans tell when a star is Tweeting for money and not just sharing information with their followers?
E! Online says that a new regulation requires celebs to disclose whether a blog post or social media post was driven by any kind of cash incentive and violators could face fines up to $11,000.
Tweets arranged through Ad.ly all include language indicating that the communication is an ad, but if the stars Tweet for cash on their own and fail to disclose it they'd be in breach of the regulations.