A police civil service commission created under this chapter may be abolished as follows: (1) by the voters in accordance with section 419.17; or (2) by a unanimous vote of the city council. Abolition by the voters shall be initiated by a petition signed by at least 25 percent of the number of legal voters voting at the last general municipal election filed with the governing body of the city requesting that the following question be submitted to the voters: “Shall the police civil service commission be abolished?”