14 CFR § 305.7 - Issuance of investigation subpenas.
(a) The Deputy General Counsel, the DOT decisionmaker, the chief administrative law judge or the administrative law judge designated to preside at the reception of evidence, may issue a subpena directing the person named therein to appear before a designated administrative law judge at a designated time and place to testify or to produce documentary evidence relating to any matter under investigation, or both. Each such subpena shall briefly advise the person required to testify or submit documentary evidence of the purpose and scope of the investigation, and a copy of the order initiating the investigation shall be attached to the subpena.
(b) Witnesses subpenaed to appear shall be paid the fees and mileage prescribed in § 302.7 of the Rules of Practice (14 CFR 302.7). Service of such subpenas shall be made in accordance with the provisions of § 302.27(c) of the Rules of Practice (14 CFR 302.27(c)).