Wis. Stat. § 779.29
In an action for the enforcement of a lien upon property under s. 779.18 a person not a party may, at any time before sale of the property upon which a lien is claimed, become a party defendant by filing with the clerk of the court where the action is pending an affidavit made in behalf of or by the person that the person is the owner of or of some interest in the property upon which a lien is claimed and believes that the claim for lien is invalid. Upon filing this affidavit the person may defend this action so far as a claim for a lien is concerned. If judgment has been previously rendered for a lien, the person may move the court for relief from the judgment within 20 days after the filing of the affidavit. The right to file an affidavit shall not extend beyond one year from the rendition of the judgment.
Wis. Stat. § 779.29