Wis. Stat. § 91.50: Exemption from special assessments.

(1) Except as provided in sub. (3), no political subdivision, special purpose district, or other local governmental entity may levy a special assessment for sanitary sewers or water against land in agricultural use, if the land is located in a farmland preservation zoning district.

(2) A political subdivision, special purpose district, or other local governmental entity may deny the use of improvements for which the special assessment is levied to land that is exempt from the assessment under sub. (1).

(3) The exemption under sub. (1) does not apply to an assessment that an owner voluntarily pays, after the assessing authority provides notice of the exemption under sub. (1).