Sixty-day notice of intention to strike

It shall be unlawful for any employee or representative of any craft, class or group of employees of a public utility to institute, participate in or aid in the conduct of a strike or work stoppage or for a public utility or any officer, agent or representative thereof to institute, participate in or aid in any lockout until sixty days shall have elapsed after written notice of intention to institute, participate or aid in the conduct of a strike or work stoppage or lockout has been served by the employee or representative intending to institute, participate in or aid in a strike or work stoppage or the public utility intending to institute, participate in or aid in a lockout upon the State Board of Mediation and the other party to the dispute. Said notice may be served on or after but not before the termination of the collective bargaining agreement between the parties and in cases where no such collective bargaining agreement exists, may be served at or after but not before the expiration of the notice of desired changes required to be served under the provisions of the act which this act supplements. During the aforementioned sixty-day period it shall be the duty of all parties to continue their endeavors in good faith to reach an agreement and said sixty-day period may be extended by written agreement of the parties, filed with the State Board of Mediation.