Wis. Stat. § 757.36
Any person having or claiming a right of action, sounding in tort or for unliquidated damages on contract, may contract with any attorney to prosecute the action and give the attorney a lien upon the cause of action and upon the proceeds or damages derived in any action brought for the enforcement of the cause of action, as security for fees in the conduct of the litigation; when such agreement is made and notice thereof given to the opposite party or his or her attorney, no settlement or adjustment of the action may be valid as against the lien so created, provided the agreement for fees is fair and reasonable. This section shall not be construed as changing the law in respect to champertous contracts.
Wis. Stat. § 757.36
An allegation of a retainer is not sufficient to imply an agreement for a lien; even if a written retainer agreement exists, there must be separate proof of a lien agreement. Weigel v. Grimmett, 173 Wis. 2d 263, 496 N.W.2d 206 (Ct. App. 1992). This section does not create an attorney's lien on settlement proceeds in the absence of a contractual lien; if the contract is breached by the attorney an alternative lien is not created. McBride v. Wausau Insurance Co., 176 Wis. 2d 382, 500 N.W.2d 387 (Ct. App. 1993).