Viacom has sued Google for $1bn (£517m) over what it claims is "massive intentional copyright infringement" on YouTube and has asked for an injunction to stop any more of its videos being uploaded to the site.
This is the first major lawsuit to be filed against Google since its acquisition of YouTube, although it was not entirely unexpected.
A statement from Viacom said:
"[YouTube's] business model, which is based on building traffic and selling advertising off of unlicensed content, is clearly illegal and is in obvious conflict with copyright laws."
The statement also criticised Google's failure to proactively deal with copyright infringement. Last week, Microsoft attacked Google for its 'cavalier' attitude to copyright.
Viacom had been in negotiations with Google over a content deal, before halting negotiations and demanding the removal of its clips. It has since struck an agreement with new internet TV service Joost.