28 USC 2502 - Aliens privilege to sue

(a) Citizens or subjects of any foreign government which accords to citizens of the United States the right to prosecute claims against their government in its courts may sue the United States in the United States Court of Federal Claims if the subject matter of the suit is otherwise within such courts jurisdiction.
(b) See section 7422(f) of the Internal Revenue Code of 1986 for exception with respect to suits involving internal revenue taxes.