Universal Music Group said on Tuesday it has filed lawsuits against video-sharing sites Grouper and Bolt.com for allowing users to swap pirated versions of its musicians' videos. Universal, whose artists include U2, Mary J Blige and Mariah Carey, said it is seeking damages up to as much as $150,000 for each incident of plus costs.

It estimated that thousands of music videos were being viewed on both sites, to their benefit alone. Grouper and Bolt.com "cannot reasonably expect to build their business on the backs of our content and the hard work of our artists and songwriters without permission and without compensating the content creators," a Universal spokesman said.

The lawsuits were filed late on Monday at the U.S. District Court, Central District of California, Western Division.

The suits accuse Grouper Network, which Sony Pictures Entertainment agreed to buy in August, and privately held Bolt.com of actively participating in the infringement by copying, reformatting, distributing and creating derivative works from Universal's musicians. The lawsuit also made clear that Universal, which is owned by French media company Vivendi, will retain the right to add Sony Pictures, a unit of Sony to the suit going forward.

They charge both Grouper and Bolt.com with "mass infringement" of Universal's copyright, comparing it with the practices of original file-sharing sites Napster and Kazaa that have both been made to pay damages in similar cases. "Through its use and exploitation of copyrighted material.

..Grouper has become one of the most prominent and valuable Web sites on the Internet," the related lawsuit says.

Grouper and Bolt.com are smaller rivals to online video-sharing service YouTube.com, which has agreed to be .

Universal Chief Executive Doug Morris had pointed to services like YouTube in the past as examples of costly copyright infringement. But the on the day its acquisition was announced. According to online audience measurement firm comScore, Bolt.

com had 8.1 million unique visitors in August while Grouper had just 1.8 million visitors.

YouTube had 72.1 million visitors in the same month.