A person, employer or labor organization desiring to intervene in any proceeding shall file with the director or designated administrative law judge a verified written application and three copies thereof, setting forth the facts upon which such person, employer or organization claims an interest in the proceeding. Such application must be served on all parties. Applications must be filed with the director or designated administrative law judge with proof of service at least two days before the first hearing. Failure to serve or file such application, as above provided, shall be deemed sufficient cause for the denial thereof, unless good and sufficient reason exists why it was not served or filed as herein provided. The director or designated administrative law judge shall rule upon all such applications and may permit intervention to such an extent and upon such terms as he shall determine may effectuate the policies of SERA.