In any action brought by or on behalf of the United States under section 1972 of this title, subpenas for witnesses may run into any district, but no writ of subpena may 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 prior permission of the trial court upon proper application and cause shown.

(Pub. L. 91–607, title I, §106(d), Dec. 31, 1970, 84 Stat. 1767.)