Families of three people killed in the Orlando nightclub massacre are suing Facebook, Google and Twitter, claiming the gunman who killed their loved ones was radicalised through propaganda he found on social media.
The families of Tevin Crosby, Juan Ramon Guerrero Jr and Javier Jorge-Reyes filed the lawsuit on Monday at a federal court in Michigan.
The complaint said the companies should be doing more to stop Islamic State (IS) from using their platforms.
During the June rampage at the Pulse nightclub in Orlando, Florida, gunman Omar Mateen pledged allegiance to IS.
Forty-nine people were killed in the worst mass shooting in modern US history.
Facebook said in a statement the company "takes swift action" to remove terrorist content when it is reported.
A similar lawsuit against Twitter was dismissed in August.