Arianna Huffington, her website and AOL were on the receiving end of a $105m (£64.5m) lawsuit by a group of angry bloggers unhappy that she sold the Huffington Post for $315m without them being paid a penny.

The class action is led by Jonathan Tasini, a writer and trade unionist, who wrote more than 250 posts for Huffington Post on an unpaid basis until he dropped out shortly after the news and comment site was sold to AOL earlier this year.

Tasini complained that "Huffington bloggers have essentially been turned into modern day slaves on Arianna Huffington's plantation" and said he was bringing the action because "people who create content ... have to be compensated" for their efforts.

The complainant and his lawyers estimate about 9,000 people wrote for the Huffington Post on an unpaid basis – and argue that their writings helped contribute about a third of the sale value of the site, the basis of their $105m claim for compensation.

Tasini was behind a successful lawsuit on behalf of freelance journalists against the New York Times a decade ago. He won a 2001 supreme court judgment that concluded copyright for print and online versions of an article were separate – meaning writers have to assign permission for a publisher to use both.

Huffington Post was founded in 2005 by Huffington and Ken Lerer – initially recruiting some high-profile writers such as Alec Baldwin and Larry David. But their ranks were swelled by a team of less well-known unpaid bloggers to boost output.

Their combined efforts helped improve traffic and revenues – which totalled $31m last year – until the site became a takeover target for AOL. Huffington and Lerer are thought to have taken the lion's share of the $315m payout, although the exact amounts has not been disclosed.

The Huffington Post said any class action lawsuit would be "completely baseless". In a statement, the website said: "Our bloggers utilise our platform to connect and ensure that their ideas and views are seen by as many people as possible. It's the same reason hundreds of people go on TV shows – to broadcast their views to as wide an audience as possible."

Last month, when visiting London, Huffington defended her policy further. She said "there's got to be a distinction between everybody who works for a media company and everybody who blogs for a media company", and noted that all media organisations depended on unpaid contributions. "If people go on Newsnight, they don't get paid," she added.

However, Tasini promised to wage a passionate campaign, saying he was "pissed off and angry" and that he would "picket her home" in his campaign. New York law firm Kurzon Strauss is advising Tasini on the suit, which has been filed in the southern district court of New York.

A spokesman for the Huffington Post said the lawsuit was without merit. He added: "Bloggers use our platform – as well as other unpaid group blogs across the web – to connect and help their work be seen by as many people as possible. It's the same reason people go on TV shows: to promote their views and ideas. HuffPost bloggers can cross-post their work on other sites, including their own."

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