Unless required for the disposition of an ex parte matter authorized by law or as expressly authorized by this section, during the pendency of a contested case either at SOAH or before the commission or executive director, a party, person, or representative of a party or person is prohibited from communicating directly or indirectly with any commissioner, the executive director, or the judge, concerning any issue of fact or law relative to the pending case, except after notice and with the opportunity for all parties to participate. For the purpose of using the special skills or knowledge of the department and its staff in evaluating the evidence, a commissioner, the executive director, or the judge may communicate ex parte with a department employee who has not participated in a hearing in the case without providing notice of the communication to the parties.