Ruling [US] ¦ Anti-Terrorism Act (ATA): Twitter, Inc. v. Taamneh

Twitter, Inc. v. Taamneh: Supreme Court Clarifies Aiding-and-Abetting Liability Under the Anti-Terrorism Act

Since 2016, plaintiffs have increasingly used “aiding and abetting” theories to hold multinational companies liable under the Anti-Terrorism Act (ATA) for terrorist acts conducted by groups such as ISIS. These claims have involved various industries including technology, social media, pharmaceuticals, telecommunications, construction, and banking. However, courts have applied varying tests on what constitutes “aiding and abetting” terrorism. The Supreme Court’s decision in Twitter, Inc. v. Taamneh marks a significant step in clarifying the legal standard for aiding-and-abetting liability under the ATA.

The Case: Twitter v. Taamneh

The case arose from a 2017 ISIS terrorist attack on the Reina nightclub in Istanbul, Turkey, which resulted in 39 deaths including Nawras Alassaf. The Alassaf family sued major social media companies — Facebook, Twitter, and Google — alleging that these platforms aided and abetted ISIS by allowing the group to use their services to spread propaganda and recruit members.

The plaintiffs argued these platforms provided “substantial assistance” by enabling ISIS’s use of recommendation algorithms to disseminate content and profit from advertisements placed alongside ISIS content. However, there was no allegation that ISIS used these platforms to plan or directly coordinate the attack.

Legal Framework for Aiding and Abetting under the ATA The ATA allows U.S. nationals injured by acts of international terrorism to sue not only the terrorists themselves but also anyone who “aids and abets, by knowingly providing substantial assistance” such acts.

The Supreme Court referred to the 1983 Halberstam v. Welch decision to define aiding-and-abetting liability. Halberstam established a framework requiring a plaintiff to prove:

1. A wrongful act causing injury was committed by the principal.
2. The defendant was generally aware of their role in an illegal or tortious activity.
3. The defendant knowingly and substantially assisted the principal violation.

Six factors from Halberstam help determine whether assistance is “substantial”: nature of the act assisted, amount of assistance, presence at the time of the tort, relationship to the tortfeasor, state of mind, and duration of assistance.

However, the Supreme Court emphasized that Halberstam’s framework is flexible and must be adapted rather than rigidly applied.

Bastian Schwind-Wagner_Follow "The Supreme Court's unanimous decision in Twitter v. Taamneh clarifies that aiding-and-abetting liability under the Anti-Terrorism Act requires conscious and culpable participation directly connected to a specific terrorist act. Passive provision of platforms or general awareness of terrorist use does not meet this high standard."

Key Clarifications by the Supreme Court

The Supreme Court in Taamneh clarified three major points:

1. More Than General Awareness Required:

   Liability requires conscious and culpable participation that helps the terrorist act succeed — not just general awareness of terrorist activities

2. Active Participation Is Necessary:

   Passive involvement or mere provision of a platform is insufficient for liability. The defendant must actively participate in or facilitate the wrongful act (e.g., giving verbal encouragement or physically assisting).

3. Nexus to Specific Attack:

   A plaintiff must show that the defendant aided and abetted a particular terrorist attack, not just a terrorist enterprise in general. Liability for all attacks by a group requires evidence that the defendant systematically and pervasively assisted that group’s operations akin to a near-common enterprise.

Application to Social Media Companies

The Court found that social media companies’ relationships with ISIS and the Reina attack were highly attenuated:

• These platforms serve billions of users globally, with content uploaded constantly.
• There was no allegation that these companies treated ISIS differently from other users.
• There was no evidence that ISIS used these platforms to plan or implement the Reina attack.
• The recommendation algorithms operated agnostically, matching content to users without specific intent.
• The companies did not encourage or advise the attack.
• Allegations of failure to remove ISIS content did not amount to active assistance.
• Holding these companies liable would effectively impose liability for every ISIS attack worldwide.

Thus, plaintiffs failed to allege knowing and substantial assistance sufficient to establish aiding-and-abetting liability.

Implications for Future Cases

The ruling raises the bar for plaintiffs pursuing aiding-and-abetting claims under the ATA:

• Plaintiffs must allege defendants had a culpable state of mind — a conscious intent to participate in the wrongful act.
• They must show a direct nexus between defendants’ assistance and a specific terrorist attack.
• Liability for aiding an entire terrorist enterprise requires evidence of pervasive and systemic support akin to conspiracy.

This decision protects companies providing broadly available (communication) services from expansive secondary liability based on passive knowledge or failure to act.

Dive deeper

• Supreme Court ¦ Proceedings and Orders ¦ Link

The amici curiae brief submitted by the Institute of International Bankers, the European Banking Federation, and the Bank Policy Institute supports Twitter in the Supreme Court case Twitter, Inc. v. Taamneh.