Unless required for the disposition of ex parte matters authorized by law, members or employees of an agency assigned to render a decision or to make findings of fact and conclusions of law in an individual proceeding shall not communicate, directly or indirectly, in connection with any issue of fact, with any person or party, nor, in connection with any issue of law, with any party or his representative, except upon notice and opportunity for all parties to participate. An agency member (1) may communicate with other members of the agency, and (2) may have the aid and advice of one or more personal assistants.