N.Y. Comp. Codes R. & Regs. tit. 12 § 263.51
A person, employer, or labor organization desiring to intervene in any proceeding shall file electronically with the director of PEPR or designated hearing officer (see section 263.15 of this Part) a written application, setting forth the facts upon which such person, employer or organization claims an interest in the proceeding. The application may be supported by a declaration of the filer. Such application must be served on all parties. Applications must be filed with the director of PEPR or designated hearing officer with proof of service at least two working 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 of PEPR or designated hearing officer shall rule upon all such applications and may permit intervention to such an extent and upon such terms as they shall determine may effectuate the policies of FLFLPA and, where applicable, of SERA.
N.Y. Comp. Codes R. & Regs. Tit. 12 § 263.51