California Code, Labor Code - LAB § 4907

(a) The privilege of any person, except attorneys admitted to practice in the Supreme Court of the state, to appear in any proceeding as a representative of any party before the appeals board, or any of its workers' compensation administrative law judges, may, after a hearing, be removed, denied, or suspended by the appeals board for either of the following:

(b) For purposes of this section, nonattorney representatives shall be held to the same professional standards of conduct as attorneys.