The legislative or governing body of every public agency having employees in positions covered by a retirement system who are ineligible to become members of such retirement system may upon the affirmative vote of a majority of the eligible employees of any coverage group of such public agency of which the employees who are ineligible to be members of such retirement system are a part, make formal application to the board for inclusion of the eligible employees of such coverage group in the said agreement; provided, that the terms of the agreement do not already apply to said positions.