The father of a young woman killed in the Paris massacre last November is suing Google, Facebook and Twitter, claiming that the companies provided “material support” to extremists in violation of the law.

Reynaldo Gonzalez, whose daughter Nohemi was among 130 people killed in the Paris attacks, filed the suit last Tuesday in the U.S. District Court in the Northern District of California. The suit claims the companies “knowingly permitted” the Islamic State group, referred to in the complaint as “ISIS,” to recruit members, raise money and spread “extremist propaganda” via their social-media services.

In statements, Facebook and Twitter said the lawsuit is without merit, and all three companies cited their policies against extremist material. Twitter, for instance, said that it has “teams around the world actively investigating reports of rule violations, identifying violating conduct, and working with law enforcement entities when appropriate.”

Facebook’s statement read, in part, that if the company sees “evidence of a threat of imminent harm or a terror attack, we reach out to law enforcement.”

Google, meanwhile, said it won’t comment on pending litigation, but noted that that it has “clear policies prohibiting terrorist recruitment and content intending to incite violence and quickly remove videos violating these policies when flagged by our users.”

Under U.S. law, internet companies are generally exempt from liability for the material users post on their networks. Section 230 of the 1996 Communications Decency Act provides a legal “safe harbor” for companies like Twitter and Facebook; it states that “no 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.”

But it isn’t clear if that legal defense will suffice in this case. Ari Kresch, a lawyer with 1-800-LAW-FIRM who is part of the Gonzalez legal team, said in an email that the lawsuit targets social media companies because of the behavior they enabled, not what they published.

“This complaint is not about what ISIS’s messages say,” he wrote. “It is about Google, Twitter, and Facebook allowing ISIS to use their social media networks for recruitment and operations.” The complaint also alleges that Google’s YouTube shared revenue with IS from ads that ran with its videos.

Benjamin Wittes, a senior fellow at the Brookings Institution, agrees that the legal “safe harbor” might not shelter social-media companies in such cases. Twitter may not succeed in quashing a similar lawsuit —filed in January by the widow of a U.S. man killed in an attack in Jordan—on those grounds, Wittes argues. But he said Twitter could still prevail because the causal link between its alleged support for extremists and the attack is very weak.