After the matter is called for hearing and before the date set for the hearing to begin, any person may petition for leave to intervene. The petition is to be served on the administrative law judge. The petition must set forth the reasons why the petitioner alleges he/she is entitled to intervene. The petition must be served on all parties in accordance with § 386.31. Any party may file a response within 10 days of service of the petition. The administrative law judge shall then determine whether to permit or deny the petition. The petition will be allowed if the administrative law judge determines that the final decision could directly and adversely affect the petitioner or the class he/she represents, and if the petitioner may contribute materially to the disposition of the proceedings and his/her interest is not adequately represented by existing parties. Once admitted, a petitioner is a party for the purpose of all subsequent proceedings.