California Code, Labor Code - LAB § 5270.5

(a) The presiding workers' compensation judge at each district office shall prepare a list of all eligible attorneys who apply to be placed on the list of eligible arbitrators. Attorneys are eligible to become arbitrators if they are active members of the California State Bar Association and are one of the following:

(b) No attorney shall be included in a panel of arbitrators, if he or she has served as a judge in any proceeding involving the same case, or has represented, or whose firm has represented, any party in the same case.