Via EFF.org:

Over a period of twelve hours, between this Thursday night and Friday morning, American Rights Counsel LLC sent out over 4000 DMCA takedown notices to YouTube, all making copyright infringement claims against videos with content critical of the Church of Scientology. Clips included footage of Australian and German news reports about Scientology, A Message to Anonymous/Scientology , and footage from a Clearwater City Commission meeting. Many accounts were suspended by YouTube in response to multiple allegations of copyright infringement.

YouTube users responded with DMCA counter-notices. At this time, many of the suspended channels have been reinstated and many of the videos are back up. Whether or not American Rights Counsel, LLC represents the notoriously litigious Church of Scientology is unclear, but this would not be the first time that the Church of Scientology has used the DMCA to silence Scientology critics. The Church of Scientology DMCA complaints shut down the YouTube channel of critic Mark Bunker in June, 2008. Bunker’s account, XenuTV, was also among the channels shut down in this latest flurry of takedown notices.