The governing body shall not include in this system any group if a majority of its members voted to disapprove the proposed plan or if two-thirds of those of its members who are also members of an existing local retirement pension or annuity fund or system do not vote for approval of the proposed plan. If there are no members of any group when the election is held, the governing body may include the group in this system, and members subsequently entering the group shall become members of this system under the provisions of this part.