Wis. Stat. § 103.455

No employer may make any deduction from the wages due or earned by any employee, who is not an independent contractor, for defective or faulty workmanship, lost or stolen property or damage to property, unless the employee authorizes the employer in writing to make that deduction or unless the employer and a representative designated by the employee determine that the defective or faulty workmanship, loss, theft or damage is due to the employee’s negligence, carelessness, or willful and intentional conduct, or unless the employee is found guilty or held liable in a court of competent jurisdiction by reason of that negligence, carelessness, or willful and intentional conduct. If any deduction is made or credit taken by any employer that is not in accordance with this section, the employer shall be liable for twice the amount of the deduction or credit taken in a civil action brought by the employee. Any agreement entered into between an employer and employee that is contrary to this section shall be void. In case of a disagreement between the 2 parties, the department shall be the 3rd determining party, subject to any appeal to the court. Section 111.322 (2m) applies to discharge and other discriminatory acts arising in connection with any proceeding to recover a deduction under this section.