39 C.F.R. § 962.16
If a Respondent believes, in good faith, that the Reviewing Official or Presiding Officer should be disqualified because of personal bias, or other reason, the Respondent may file a timely and sufficient affidavit alleging such belief with supporting evidence. If the Presiding Officer finds that such allegations concerning the Reviewing Official are meritorious, he may direct the Reviewing Official to disqualify himself and request the appointment of a new Reviewing Official. Where a Respondent seeks the disqualification of a Presiding Officer, such Presiding Officer, may, in his discretion, disqualify himself at any time during the proceeding. In the event a Reviewing Official or Presiding Officer withdraws from a hearing, the proceeding shall be stayed until the assignment of a new Reviewing Official or Presiding Officer.
39 C.F.R. §962.16