(1) All employees of the State of Nebraska or any political subdivision thereof or any instrumentality jointly created by this state and any other state or states who have heretofore been excluded from receiving or qualifying for benefits under Title II of the Social Security Act because of membership in a retirement system may, when sections 68-621 to 68-630 have been complied with, vote at a referendum upon the question of whether service in positions covered by such retirement system should be excluded from or included under the state agreement, except that if such a referendum has been conducted and certified in accordance with section 218(d)(3) of the Social Security Act, as amended in 1954, prior to May 18, 1955, then no further referendum shall be required, but this shall not prohibit the conducting of such further referendum.

(2) The Governor may authorize a referendum and designate any agency or individual to supervise its conduct, in accordance with the requirements of section 218(d)(3) of the Social Security Act, on the question of whether service in positions covered by a retirement system established by the state or by a political subdivision thereof should be excluded from or included under an agreement under sections 68-601 to 68-631.