Municipal general member coverage plan 2 is applicable to a designated group of municipal general members the first day of the calendar month following an affirmative vote by the majority of the municipal general members in a designated group. A designated group may be all members employed by the affiliated public employer, an organizational group whose compensation is established by negotiated contract or all members employed by the affiliated public employer whose compensation is not established by negotiated contract. The election shall be conducted by the retirement board in accordance with procedures adopted by the retirement board. The procedures shall afford all municipal general members who are part of the designated group an opportunity to vote. A new election for coverage by municipal general member coverage plan 2 shall not be held prior to the expiration of six months following the date of an election which failed to adopt municipal general member coverage plan 2. An election adopting municipal general member coverage plan 2 is irrevocable for the purpose of subsequently adopting a coverage plan which would decrease employer or employee contributions with respect to all current and future municipal general employees of the affiliated public employer who are part of the designated group.