27 C.F.R. § 771.98
Administrative law judges shall perform no functions inconsistent with their duties and responsibilities. The Director may assign administrative law judges duties not inconsistent with the performance of their functions as administrative law judges. Except to the extent required for the disposition of ex parte matters as required by law, no administrative law judge shall consult any person or party as to any fact in issue unless there has been notice and opportunity for all parties to participate. The functions of the administrative law judge shall be entirely separated from the general investigative functions of the agency. No officer, employee, or agent engaged in the performance of investigative or prosecuting functions in any proceeding shall, in that proceeding or a factually related proceeding, participate or advise in the administrative law judge's or Director's decision, or in the agency review on appeal, except as a witness or counsel in the proceedings. The administrative law judge may not informally obtain advice or opinions from the parties or their counsel, or from any officer or employee of the ATF, as to the facts or the weight or interpretation to be given to the evidence. The administrative law judge may, however, informally obtain advice on matters of law or procedure in a proceeding from officers or employees who were not engaged in the performance of investigative or prosecuting functions in that proceeding or a factually related proceeding. The administrative law judge may, at any time, consult with and obtain instructions from the Director on questions of law and policy. Furthermore, it is not a violation of the separation of functions for the administrative law judge to participate in the questioning of witnesses, where the questioning is for clarification or to move the proceedings along, and where the questioning is not so extensive as to place the administrative law judge in the position of a prosecuting officer.
27 C.F.R. §771.98