Whenever electors of any city under the city manager plan of government, equal in number to thirty percent of those who voted at the last regular city election, shall file a petition with the city clerk, asking that the question of abandoning the city manager plan of government be submitted to the electors thereof, the city clerk shall within one week certify that fact to the city council, and the city council shall, within thirty days, adopt a resolution to provide for submitting such question at the next regular municipal election after adoption of the resolution. When such a petition is filed with the city clerk within a seventy-day period prior to a regular municipal election, the resolution adopted by the city council shall provide for the submission of such question at the second regular municipal election thereafter as provided by law.