43 U.S. Code § 103 - Witnesses’ fees
Witnesses shall have the right to receive their fee for one day’s attendance and mileage in advance. The fees and mileage of witnesses shall be the same as that provided by law in the district courts of the United States in the district in which such land offices are situated; and the witness shall be entitled to receive his fee for attendance in advance from day to day during the hearing.
Source(Jan. 31, 1903, ch. 344, § 2,32 Stat. 790.)