Viacom is suing the Google-owned site for damages concerning 150,000 copyrighted clips which appear on the site. Viacom is alleging that YouTube has done "little or nothing" to stop infringement and consistently allowed the videos of popular TV programmes such as 'South Park', 'MTV Unplugged' and the climate-change documentary 'An Inconvenient Truth', to be posted and viewed repeatedly on the website.
However, the search giant’s lawyers claim YouTube has complied with the 1998 Digital Millennium Copyright Act and have handled claims of infringement correctly.
In US court papers, Google said YouTube "goes far beyond its legal obligations in assisting content owners to protect their works".
Google also claims the action "threatens the way hundreds of millions of people legitimately exchange information" over the web.
"The availability on the YouTube site of a vast library of the copyrighted works of plaintiffs and others is the cornerstone of defendants' business plan," Viacom said.
Viacom chairman Sumner Redstone added: "We cannot tolerate any form of piracy by anyone, including YouTube... it cannot get away with stealing our products."
Immediately after the legal action was started, YouTube launched an antipiracy tool that checks uploaded videos against the original content in an effort to flag piracy.