28 USC 1781 - Transmittal of letter rogatory or request

(a) The Department of State has power, directly, or through suitable channels
(1) to receive a letter rogatory issued, or request made, by a foreign or international tribunal, to transmit it to the tribunal, officer, or agency in the United States to whom it is addressed, and to receive and return it after execution; and
(2) to receive a letter rogatory issued, or request made, by a tribunal in the United States, to transmit it to the foreign or international tribunal, officer, or agency to whom it is addressed, and to receive and return it after execution.
(b) This section does not preclude
(1) the transmittal of a letter rogatory or request directly from a foreign or international tribunal to the tribunal, officer, or agency in the United States to whom it is addressed and its return in the same manner; or
(2) the transmittal of a letter rogatory or request directly from a tribunal in the United States to the foreign or international tribunal, officer, or agency to whom it is addressed and its return in the same manner.