Wis. Stat. § 8.37

Unless otherwise required by law, all proposed constitutional amendments and any other measure or question that is to be submitted to a vote of the people, or any petitions requesting that a measure or question be submitted to a vote of the people, if applicable, shall be filed with the official or agency responsible for preparing the ballots for the election no later than 42 days prior to the election at which the amendment, measure or question will appear on the ballot.