International Organizations Immunities Act (IOIA), 22 U.S.C. 288

For the purposes of this subchapter, the term "international organization" means a public international organization in which the United States participates pursuant to any treaty or under the authority of any Act of Congress authorizing such participation or making an appropriation for such participation, and which shall have been designated by the President through appropriate Executive order as being entitled to enjoy the privileges, exemptions, and immunities provided in this subchapter.