Quick search by citation:

22 U.S. Code § 288d - Privileges, exemptions, and immunities of officers, employees, and their families; waiver

Persons designated by foreign governments to serve as their representatives in or to international organizations and the officers and employees of such organizations, and members of the immediate families of such representatives, officers, and employees residing with them, other than nationals of the United States, shall, insofar as concerns laws regulating entry into and departure from the United States, alien registration and fingerprinting, and the registration of foreign agents, be entitled to the same privileges, exemptions, and immunities as are accorded under similar circumstances to officers and employees, respectively, of foreign governments, and members of their families.
Representatives of foreign governments in or to international organizations and officers and employees of such organizations shall be immune from suit and legal process relating to acts performed by them in their official capacity and falling within their functions as such representatives, officers, or employees except insofar as such immunity may be waived by the foreign government or international organization concerned.
(Dec. 29, 1945, ch. 652, title I, § 7(a), (b), 59 Stat. 671.)