35 U.S.C. § 24

The clerk of any United States court for the district wherein testimony is to be taken for use in any contested case in the Patent and Trademark Office, shall, upon the application of any party thereto, issue a subpoena for any witness residing or being within such district, commanding him to appear and testify before an officer in such district authorized to take depositions and affidavits, at the time and place stated in the subpoena. The provisions of the Federal Rules of Civil Procedure relating to the attendance of witnesses and to the production of documents and things shall apply to contested cases in the Patent and Trademark Office. Every witness subpoenaed and in attendance shall be allowed the fees and traveling expenses allowed to witnesses attending the United States district courts. A judge of a court whose clerk issued a subpoena may enforce obedience to the process or punish disobedience as in other like cases, on proof that a witness, served with such subpoena, neglected or refused to appear or to testify. No witness shall be deemed guilty of contempt for disobeying such subpoena unless his fees and traveling expenses in going to, and returning from, and one day’s attendance at the place of examination, are paid or tendered him at the time of the service of the subpoena; nor for refusing to disclose any secret matter except upon appropriate order of the court which issued the subpoena.