Iowa Code § 49A.4: Submission at general election.

Whenever a public measure has passed the general assembly which under the Constitution must be submitted to a vote of the entire people of the state and no time is fixed by the Constitution or legislature for such submission, or whenever a proposition to amend the Constitution has been adopted by two succeeding general assemblies and no time is fixed by the last general assembly adopting the same for its submission to the people, said measure or amendment shall be submitted to the people at the ensuing general election, in the manner required by law.