The fees of more than four witnesses shall not be taxed against the United States, in the examination of any criminal case before a United States magistrate judge, unless their materiality and importance are first approved and certified to by the United States attorney for the district in which the examination is had.
(June 25, 1948, ch. 646, 62 Stat. 956; Pub. L. 90–578, title IV, § 402(b)(2), Oct. 17, 1968, 82 Stat. 1118; Pub. L. 101–650, title III, § 321, Dec. 1, 1990, 104 Stat. 5117.)