Iowa Code § 73A.13: Objections.

At any time before the date fixed for the issuance of such bonds or other evidence of indebtedness, interested objectors in any municipality equal in number to one percent of those voting for the office of president of the United States or governor, as the case may be, at the last general election in said municipality, but in no event less than twenty-five, may file a petition in the office of the clerk or secretary of the municipality setting forth their objections thereto.