Families of three victims of the Pulse gay club massacre have launched a lawsuit against Facebook, Twitter, and Google – in a bid to hold media companies responsible for the spread of ISIS propaganda.

49 people died and more than 50 were injured in the Orlando massacre on June 12, when gunman Omar Mateen opened fire during a Latin night at the Florida gay club. The majority of the victims were LGBT people of colour.

Transcripts of 911 calls made by terrorist Omar Mateen from inside the club revealed he pledged allegiance to ISIS, and cited acts of US aggression as his motivation.

After Mateen’s attack, the FBI determined his computer had been used to consume ISIS propaganda, amid fears about the role of the internet in radicalising young people. Mateen watched extremist videos including beheadings, which were easily found online.

This week, the families of three men who died in the attack – Tevin Crosby, Javier Jorge-Reyes, and Juan Ramon Guerrero – brought legal action against internet giants Twitter, Facebook and Google, alleging they failed to stop the spread of extremist ISIS materials.

ISIS militants operate via a network of accounts across social media, spreading messages via Facebook,Twitter and YouTube. While some materials are flagged and removed, critics say the social media giants have failed to tackle the full scale of the problem.

The lawsuit states: “Without Defendants Twitter, Facebook, and Google (YouTube), the explosive growth of ISIS over the last few years into the most feared terrorist group in the world would not have been possible.”

Juan Guerrero, the father of one of the victims, told Fox: “I wish we could get some regulations put in place. They have to do something to prevent these people from doing things like this.

“Life has not been easy for me or my whole family. It is something I remember and have to live with every day.”

However, the case will have to overcome some serious hurdles, due to a provision of the 1996 Communications Decency Act (CDA).

Section of 230 of the CDA 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” – a precedent that will have to be overturned if the case is to succeed, as it protects Facebook from liability for users’ posts.

Facebook, Twitter, or Google have not yet responded to the lawsuit.