If an election is conducted pursuant to § 1-22, no further election shall be held for an exclusive representative of the employees in the unit in which said election was conducted for a period of 2 years from the date of the School Board’s certification of the results of said election. Subsequent elections may be held upon the filing of a petition with the School Board, supported by 30% or more of the employees of an appropriate unit, alleging that the said employees in said unit desire:that an employee organization be selected as their exclusive representative; that an employee organization’s certification as exclusive representative be rescinded; or that another employee organization be certified as their exclusive representative. The School Board may, upon verifying the requisite percentage, determine by secret ballot election which employee organization, if any, shall be the exclusive representative of such employees; provided, however, that no valid election shall have been conducted in said unit within the preceding 2 years. City Code, 1976/83, art. 24, §18(c), (d) Ord. 67-1031