The Alien Tort Statute, 28 U.S.C. § 1350, gives United States district courts “original jurisdiction of any civil action by an alien for a tort only, committed in violation of the law of nations or a treaty of the United States.” The statute, passed and largely overlooked, as part of the Judiciary Act of 1789, makes at least some rules of customary international law enforceable in courts. Since the landmark decision of Filartiga v. Pena-Irala, 630 F.2d 876 (2d Cir. 1980), in which the relatives of an individual tortured and killed by a Paraguayan official successfully were allowed to bring suit against that official in a United States court under the ATS claiming injury in violation of customary international law prohibition against torture, the ATS has become the principal vehicle for litigating international human rights claims in U.S. courts. ATS plaintiffs increasingly accuse large multinational companies of complicity in human rights abuses by developing country governments with which they do business.
The central difficulty of ATS litigation is ascertaining the content of customary international law. Customary international law is evolving and its content debatable. Its content is evidenced by a diverse range of sources - international agreements, state practice out of a sense of legal obligation (opinio juris), and, in at least some circumstances, the writings of international law scholars. The amorphous and consensual nature of customary international law, and the potential for ATS suits to interfere with foreign policy, means that the Supreme Court has tried to ensure that only the most solidly-established norms of customary international are actionable under the ATS. Only violations of customary international law that are as universally recognized as the “violation of safe conducts, infringement of the rights of ambassadors, and piracy” had been in 1789, give rise to cognizable ATS claims. See Sosa v. Alvarez-Machain, 542 692 (2004). Though courts may allow ATS claims based on violations of the law of nations other than those recognized in 1789, plaintiffs must allege activity that is universally recognized to be a violation of an equally “specific, universal and obligatory” legal norm. at 732. The limited range of violations of customary international law actionable under the Sosa standard includes torture, genocide, slavery and extrajudicial killing.
Other important issues in ATS litigation include the existence of derivative or corporate liability under customary international law. Neither has been decisively resolved by the Supreme Court and ATS authority is inconsistent and unevenly developed across the various federal circuits.