Changing amount of withholding by written agreement between employer and employee.

In addition to the amount required to be deducted and withheld, an employer and employee may agree in writing that an additional amount shall be withheld from the employee’s wages. The amount deducted and withheld pursuant to such an agreement shall be considered as an amount required to be deducted and withheld for all purposes of this subchapter.

In lieu of the amount required to be deducted and withheld under this section, an employer and employee may agree in writing on a form prescribed and provided by the department that a lesser amount be withheld from the employee’s wages if: 1. The employee determines that the lesser amount approximates the employee’s anticipated income tax liability for the year. 2. The employee sends a copy of the completed agreement form to the department within 10 days after it is filed with the employer. 3. The agreement expires on April 30 of the following year, for calendar year taxpayers, or 4 months following the close of their fiscal year, for fiscal year taxpayers.

If the department determines that an agreement under par. (b) would result in an insufficient amount of tax being withheld, the department may void the agreement by notification to the employer and employee.