15 U.S.C. § 23 — Suits by United States; subpoenas for witnesses

This law expands where witnesses can be subpoenaed in antitrust cases brought by or for the United States. In any suit, action, or proceeding brought by or on behalf of the United States, subpoenas for witnesses required to attend a court of the United States, in any judicial district, for any civil or criminal case arising under the antitrust laws, may run into any other district. But in civil cases there's a limit: no writ of subpoena can be issued for a witness living outside the district where the court is held, at a distance greater than 100 miles from the place of holding the court, without the trial court's permission first obtained upon a proper application and cause shown.