With respect to each retirement system coverage group, the legislative or governing body of every public agency having employees in positions covered by a retirement system, may, upon the affirmative vote of a majority of eligible retirement system employees of the retirement system coverage group at a referendum conducted in accordance with Article 2 (commencing with Section 22300) of this chapter and the rules and regulations promulgated by the board pursuant to this part, make formal application to the board for the inclusion of the employees in each retirement system coverage group in the agreement.