15 U.S.C. § 23 : US Code - Section 23: Suits by United States; subpoenas for witnesses

Search 15 U.S.C. § 23 : US Code - Section 23: Suits by United States; subpoenas for witnesses

In any suit, action, or proceeding brought by or on behalf of the
United States subpoenas for witnesses who are required to attend a
court of the United States in any judicial district in any case,
civil or criminal, arising under the antitrust laws may run into
any other district: Provided, That in civil cases no writ of
subpoena shall issue for witnesses living out of the district in
which the court is held at a greater distance than one hundred
miles from the place of holding the same without the permission of
the trial court being first had upon proper application and cause
shown.