Wis. Stat. § 74.79: Lienholder may contest tax.

(1) Any person who holds a lien on real property has the remedies of a property owner to contest, as to that property, the legality or validity of any real property tax, special assessment, special charge or special tax or the validity of a tax certificate issued under s. 74.57.

(2) A county to which a tax certificate has been issued under s. 74.57 has the remedies of a property owner to contest, as to any property included in the tax certificate, the assessed value of the property and the legality or validity of any real property tax, special assessment, special charge or special tax.