Wis. Stat. § 812.40

At any time while an earnings garnishment is in effect, the debtor and creditor may stipulate in writing to an extension of the earnings garnishment for additional pay periods. The extension may commence on the first day after the earnings garnishment ends and shall end within 13 weeks after the last day of the last pay period affected by the earnings garnishment. The garnishee shall be bound by the extension if a copy of the stipulation is delivered or mailed to the garnishee, together with the additional garnishee fee under s. 812.33 (1), before the last day of the last pay period affected by the earnings garnishment or any prior stipulated extension of the earnings garnishment. A stipulated extension is void and the garnishee fee shall be refunded if, prior to the last day of the last pay period af- 8812.40 GARNISHMENT fected by the earnings garnishment, the garnishee is served under s. 812.35 (3) by a creditor seeking to satisfy a different judgment against the debtor.