MySpace on Wednesday stepped up a contentious campaign to block other online companies from trying to make money from its burgeoning audience when it barred its users from linking to some content on a rival website from their MySpace pages.

The move by the News Corp-owned social networking site was the most visible yet in an effort to prevent others advertising or selling direct to its audience. However, it also intensified complaints in Silicon Valley that the media company was adopting a “closed” approach to its online community that would restrict freedom of expression and limit technological experimentation.

The latest dispute sprang from a decision to block MySpace users from linking to material on Photobucket, a fast-growing website where users can upload their own videos and photos.

In a statement, MySpace said Photobucket had been encouraging its users to display their pictures in an ad-sponsored slideshow – an apparent reference to a promotion for the forthcoming Spider-Man 3 film. While links to photos were still allowed, all videos and slideshows were blocked because it was impossible to single out the offending material, according to a person familiar with the dispute.

That echoed earlier moves by MySpace to bar Revver, another ad-supported video site, and to prevent musician Tila Tequila from promoting her own music on her website page.

The bar on ad-supported media such as this is also a potential hurdle to Google’s efforts to increase advertising on YouTube, since the hit online video site owes much of its success to its adoption by the MySpace audience.

Privately, News Corp executives have made it clear that they would act forcefully to stop other websites from trying to “build their own economies” on MySpace.

In a note to users posted on its pages, Photobucket accused MySpace of “contradicting the very belief of personal and social media” by limiting self- expression. “By severely restricting this freedom, MySpace is showing that it considers you as a commodity which it can treat as it sees fit.”

That tapped into a strong belief in Silicon Valley, and one of the foundations of the so-called Web 2.0 movement, that users should be free to mix and match services, rather than being tied into “closed” systems.