Activist groups sued Viacom Inc. on Thursday, claiming the parent of Comedy Central improperly asked the video-sharing site YouTube to remove a parody of the cable network's "The Colbert Report."

Viacom responded by saying it had no records of ever making such a request.

Although the video in question contained clips taken from the television show, MoveOn.org Civic Action and Brave New Films LLC argued that their use was protected under "fair use" provisions of copyright law.

With Viacom identified by YouTube as the source of the removal request, they said Viacom should have known the use was legal and thus its complaint to YouTube to have the video blocked amounted to a "misrepresentation" that is subject to damages under the 1998 Digital Millennium Copyright Act.

The challenge, filed in U.S. District Court in San Francisco, came about a week after Viacom filed its own, $1 billion lawsuit against YouTube, claiming that the wildly popular Web site is rife with copyrighted video from Viacom shows, including "The Colbert Report."

Neither YouTube nor its parent, Google Inc., was named in the latest lawsuit, filed on the plaintiffs' behalf by the Electronic Frontier Foundation and Stanford Law School's Center for Internet and Society.

In a letter to the plaintiffs' lawyers, Michael D. Fricklas, general counsel for Viacom, said the company had no record of sending YouTube a complaint, despite YouTube's identification of Viacom as the source. YouTube had no comment about the discrepancy.