The company behind the site will argue that it should be granted immunity under US law.
A literary agent is suing Wikipedia owner the Wikimedia Foundation over a comment posted on the site that she was "the dumbest" of a list of the 20 worst literary agents. Barbara Bauer said the comment was defamatory.
A science fiction authors' organisation called Writers Beware created a list of the 20 literary agencies about which it received the most complaints. Bauer was on that list, and she has claimed that comments on Wikipedia then called her "the dumbest of the 20 worst" agents.
Wikimedia denies that those comments ever appeared but argues that even if they did they are protected under the US Constitution's guarantee of the right to free speech.
Wikimedia argues overall, though, that it is protected from liability by the Communications Decency Act (CDA), whose section 230 protects a publisher from liability for things said by other people on its electronic services until it is made aware of the comments. At that point it must take action or risk becoming liable.
The section of the Act says that "[n]o provider or user of an interactive computer service shall be treated as the publisher or speaker of any information provided by another information content provider".
In its application for summary dismissal of the case, Wikimedia says that the law applies directly to it.
"As the operator of the Wikipedia website, Wikimedia is indisputably a user and a provider of an interactive computer service under [section] 230," said its claim.
"In addition, the statements on which Plaintiffs' claims are based were posted on Wikipedia by another information content provider.
The Complaint itself indicates that the allegedly defamatory statements on Wikipedia originated elsewhere, alleging that virtually identical statements to those appearing on the Wikipedia site appeared on numerous other websites."
The case is a vital one for Wikipedia, which exists to hold encyclopedia entries created by other people. If would be a serious blow to its way of operating if it were not granted immunity under the CDA.
"We provide a platform through Wikipedia for smart citizens to give their knowledge back to a larger culture," said Wikimedia Foundation general counsel Mike Godwin. "Our ability to offer citizens that platform is what's at stake in this case."
"Congress passed Section 230 of the Communications Decency Act in order to protect websites' operators like Wikipedia from suits like this one," said James Chadwick of Sheppard Mullin, the US law firm that is acting for Wikimedia.
"It's simple but it's fundamental: Congress has decided that internet censorship isn't the answer, so websites aren't liable for statements posted by their users."
The case is being supported by digital rights body the Electronic Frontier Foundation. "Without strong liability protection, it would be difficult for Wikipedia to continue to provide a platform for user-created encyclopedia content," said EFF senior staff attorney Matt Zimmerman.