(a) Each bargaining unit, including the bargaining units organized and represented by a labor union on the date of enactment of the act creating this chapter, shall be classified as belonging to one of the following classes:
(b) Any unit or units consisting of police officers, corrections officers, firemen, prison guards, harbor pilots, or other persons employed to protect the public safety and welfare and/or protect the property of a public employer is/are hereby classified Class III.
(c) Any unit or units consisting of public employees who maintain and operate equipment used in the production of water and power is/are hereby classified Class III.
(d) Any unit or units consisting of physicians is/are hereby classified Class III.