42 CFR 93.518 - Witnesses.
(a) Except as provided in paragraph (b) of this section, witnesses must give testimony at the hearing under oath or affirmation.
(b) The ALJ may admit written testimony if the witness is available for cross-examination, including prior sworn testimony of witnesses that has been subject to cross-examination. These written statements must be provided to all other parties under § 93.513.
(c) The parties may conduct direct witness examination and cross-examination in person, by telephone, or by audio-visual communication as permitted by the ALJ. However, a respondent must always appear in-person to present testimony and for cross-examination.
(d) The ALJ may exercise reasonable control over the mode and order of questioning witnesses and presenting evidence to -
(1) Make the witness questioning and presentation relevant to deciding the truth of the matter; and
(2) Avoid undue repetition or needless consumption of time.
(e) The ALJ must permit the parties to conduct cross-examination of witnesses.
(f) Upon request of a party, the ALJ may exclude a witness from the hearing before the witness' own testimony. However, the ALJ may not exclude -
(1) A party or party representative;
(2) Persons whose presence is shown by a party to be essential to the presentation of its case; or
(3) Expert witnesses.