§ 1922.
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].)