4. Every municipality adhering, on 31 December 1988, to the general retirement plan established by the Act respecting retirement plans for the mayors and councillors of municipalities (chapter R-16) shall be deemed to adhere to this plan unless it adopts and brings into force, before 1 July 1989, a by-law stating that it elects not to adhere to this plan.
The by-law shall have effect as of 1 January 1989. Employers and employees contributions paid from that date shall be refunded with interest computed in accordance with government regulation and at the rate determined by such regulation.
Any municipality which has stated that it elects not to adhere to this plan may adhere to it at any later time.