He's a singer who has made some odd career moves in his time, from changing his name to an unpronounceable love symbol to scrawling "slave" on his cheek in protest at his record company.

But industry experts yesterday warned that Prince's latest decision might be the most controversial of all.

He has threatened to sue thousands of his biggest fans for breach of copyright, provoking an angry backlash and claims of censorship.

His lawyers have forced his three biggest internet fansites to remove all photographs, images, lyrics, album covers and anything linked to the artist's likeness. A legal letter asks the fansites to provide "substantive details of the means by which you propose to compensate our clients [Paisley Park Entertainment Group, NPG Records and AEG] for damages".

The singer himself is believed to take a close interest in unofficial use of his image and music, monitoring websites from his sprawling Paisley Park studio complex in Minneapolis.

A coalition named Prince Fans United, representing Housequake.com, Princefans.com and Prince.org, has been formed by the website organisers to fight back. They said they would contest the action on the basis that it was an attempt "to stifle all critical commentary about Prince". They added that the "cease and desist" notices went as far as calling for the removal of pictures taken by fans of their Prince tattoos and their vehicles carrying Prince-inspired licence plates.

"It's a really short-sighted and futile move," said Nicola Slade, editor of the industry newsletter Record of the Day. "Prince has got a lot of fans and as he's decided to take a more leftfield approach to releasing his material, he should be nurturing the relationship. I'm shocked, really."

The singer had been considered to be in the vanguard of efforts by some artists to cut record labels out of the equation and forge their own relationships with fans through the web and live concerts, having been one of the first to sell music directly to fans via his website.

He recently completed a 21-night residency at London's O2 arena, effortlessly mixing up the setlist each night to draw on a rich back catalogue that includes Purple Rain, Raspberry Beret, Kiss and Sign o' the Times, and was lauded for a genius marketing move in giving away his CD to concertgoers and with copies of the Mail on Sunday.

Alex Burmaster, an analyst at Nielsen Online, said: "It's a paradox that a musician who has done so much to bring himself closer to his fans, particularly with his 'them and us' crusade against the record labels, should be engaging in a course of action that effectively removes the raison d'etre of fansites.

"But it's the mark of the man who always goes against the grain that he should be doing this at a time when other artists and their labels are suddenly embracing the social media phenomenon."

In 1993, amid a bitter dispute with the record label, Prince changed his name to an unpronounceable "love symbol" as a step towards his "ultimate goal of emancipation from the chains" that he said tied him to Warner Bros.

Yesterday's move follows an earlier declaration of war on copyrighted material hosted by web giants such as YouTube and eBay.

In September, he appointed the internet company Web Sheriff to police the removal of up to 2,000 clips from YouTube. Web Sheriff managing director, John Giacobbi, said at the time that the singer wanted "to create a template for other artists". "Prince doesn't really want to go around suing people - he'd much rather people just respected his rights. He will be victorious," he said.

Controversy followed this decision, too, when a mother from Pennsylvania posted a clip of her baby dancing to his 1984 hit Let's Go Crazy and Prince's lawyers demanded it was taken down.

Lawyers at the Electronic Frontier Foundation have vowed to contest the claim on her behalf, saying the song is hardly audible and constitutes fair use.

By going after the Google-owned YouTube, Prince was merely following the lead of a handful of other big rights owners - including MTV-owner Viacom, the estate of Elvis Presley and the Premier League - that believe the video sharing site makes advertising revenue off the back of their copyrighted content. But while some artists have resorted to the law in an attempt to persuade websites or internet providers to remove pirated songs and there have been disputes over lyrics, most decided long ago that it was counterproductive to attempt to get fans to remove images and album covers.

"You can get things taken down, the legal tools are there to do it," said Caroline Kean, a partner at the law firm Wiggin. "The reason people don't is partly practical, because there are so many images, but also due to the bad publicity you get from going after your biggest fans. Most people soon realised it was counter-productive."

A spokeswoman for the fans' campaign said the sites had always tried to work with Prince's management. But it appeared that Prince wanted to edit his past and there was "no sign" of his lawyers backing down, she said. "He's trying to control the internet 100% and you can't do that without infringing people's freedom of speech," she added.