26 U.S.C. § 7610: Fees and costs for witnesses

fees and mileage to persons who are summoned to appear before the Secretary, and reimbursement for such costs that are reasonably necessary which have been directly incurred in searching for, reproducing, or transporting books, papers, records, or other data required to be produced by summons. the person with respect to whose liability the summons is issued has a proprietary interest in the books, papers, records or other data required to be produced, or the person summoned is the person with respect to whose liability the summons is issued or an officer, employee, agent, accountant, or attorney of such person who, at the time the summons is served, is acting as such. This section applies with respect to any summons authorized under section 6420(e)(2), 6421(g)(2), 6427(j)(2), or 7602.