28 U.S.C. § 1785: Subpoenas in multiparty, multiforum actions

When the jurisdiction of the district court is based in whole or in part upon section 1369 of this title, a subpoena for attendance at a hearing or trial may, if authorized by the court upon motion for good cause shown, and upon such terms and conditions as the court may impose, be served at any place within the United States, or anywhere outside the United States if otherwise permitted by law.