Wis. Stat. § 229.53: State pledge.

The state pledges to and agrees with the bondholders, and persons that enter into contracts with a district under this subchapter, that the state will not limit or alter the rights and powers vested in a district by this subchapter, including the rights and powers under s. 229.44 (15), before the district has fully met and discharged the bonds, and any interest due on the bonds, and has fully performed its contracts, unless adequate provision is made by law for the protection of the bondholders or those entering into contracts with a district.