Oona Hathaway, Professor of International Law at Yale Law School, Professor of the Yale University Department of Political Science, Professor at the Jackson School of Global Affairs, and Director of the Yale Law School Center for Global Legal Challenges, reported Wednesday on social media that President Trump’s threats against Iran are illegal.
Hathaway, who served as Special Counsel to the General Counsel at the U.S. Department of Defense during the Obama administration, wrote on X: “I am getting questions about whether Trump’s threats alone are illegal. The answer is yes. 1. Additional Protocol I states ‘Acts or threats of violence the primary purpose of which is to spread terror among the civilian population are prohibited.’”
I am getting questions about whether Trump’s threats alone are illegal. The answer is yes.
1. Additional Protocol I states “Acts or threats of violence the primary purpose of which is to spread terror among the civilian population are prohibited.” (also DOD LOW Manual §5.2.2)
1/— Oona Hathaway (@oonahathaway) April 8, 2026
She added: “2. Threats of use of force also violate the United Nations Charter, which provides ‘Members shall refrain in their international relations from the THREAT or use of force against the territorial integrity or political independence of any state . .’
“The Vienna Convention on the Law of Treaties also provides ‘A treaty is void if its conclusion has been procured by the threat or use of force in violation of the principles of international law embodied in the Charter of the United Nations.
“Moreover, the threat to commit mass war crimes raises questions as to whether the U.S. is fighting the war consistent with its legal obligations. It gives insight into intent that may be relevant to war crimes investigations.”
When asked, “who can do something about this?”, Hathaway replied: “The short answer: Congress. I didn’t mention that all of this of course also violates the US Constitution, which gives Congress, not the President the power to declare war. They need to step up and deny funding to continue this illegal war.”
[NOTE: In 2025, Hathaway was elected president of the American Society of International Law, the nonprofit, nonpartisan, educational membership organization chartered by Congress in 1950. Its mission is to “foster the study of international law and to promote the establishment and maintenance of international relations on the basis of law and justice.”]