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.
(Oct. 15, 1914, ch. 323, §13,
The antitrust laws, referred to in text, are defined in section 12 of this title.