Broadcaster Viacom is suing Google, alleging copyright infringement by its video sharing site, YouTube, and seeking $1bn (£500m) in damages.
The lawsuit follows a request sent by Viacom to Google last month under the US Digital Millennium Copyright Act (DMCA) in relation to the unauthorised posting of Viacom videos to YouTube.
At the time, Viacom demanded that Google remove more than 100,000 of its clips from YouTube, which Google acquired last year for $1.65bn (£825m). Google said it would comply with the request.
In escalating its battle with this lawsuit, Viacom reiterated that YouTube had allowed and benefited from "massive intentional" copyright violations of Viacom videos.
In addition to $1bn damages, Viacom is asking the court for an injunction barring Google and YouTube from continuing the alleged infringement.
Google said it was ready to fight the allegations and was confident that "YouTube has respected the legal rights of copyright holders". A spokesperson said: "We will certainly not let this suit become a distraction to the continuing growth and strong performance of YouTube and its ability to attract more users, more traffic and build a stronger community."
Almost 160,000 Viacom video clips have been uploaded to YouTube without permission and have been viewed over 1.5bn times, Viacom alleged.
"YouTube is a significant, for-profit organisation that has built a lucrative business out of exploiting the devotion of fans to others' creative works in order to enrich itself and its corporate parent Google," Viacom claimed.
The broadcaster said Google and YouTube were illegally profiting from the traffic that the unauthorised videos draw to their sites by selling advertising. Viacom added that YouTube had been lax in its attempts to stop its users from uploading copyrighted videos without permission.
Viacom, which owns MTV, Nickelodeon, Comedy Central and Paramount Pictures, said it decided to sue Google after negotiations and other measures failed to halt the alleged copyright infringement.
Sheldon Klein, a lawyer specialising in intellectual property matters and a partner at US law firm Arent Fox, said the case was unlikely to result in a total shutdown of YouTube, because legitimate uses of the site existed beyond the potentially illegal activities Viacom objected to.
But Google might find itself liable if Viacom proved that Google and YouTube had not done all that was possible to prevent users from uploading copyrighted videos without permission, especially after being served with the DMCA notice last month, Klein said.
Specifically, if YouTube and Google have not implemented available technology that would allow them to do a better job of filtering out infringing videos, Viacom could have a legitimate argument in saying they were not trying hard enough, he said.
Google executives have said the company is developing technology to address the issue of downloads on YouTube that infringe copyright and have promised to deliver it in the near future.