Wis. Stat. § 108.205

(1) Each employer shall file with the department, in such form as the department by rule requires, a quarterly report showing the name, social security number and wages paid to each employee who is employed by the employer in employment with the employer during the quarter. The department may also by rule require each employer to include in the report any salary reduction amounts that are not wages and that would have been paid to each such employee by the employer as salary during the quarter but for a salary reduction agreement under a cafeteria plan, within the meaning of 26 USC 125 . The employer shall file the report no later than the last day of the month following the completion of each quarter.

(2) All employers of 100 or more employees, as determined under s. 108.22 (1) (ae) , shall file the quarterly report under sub. (1) using an electronic medium approved by the department for such employers. An employer that becomes subject to the reporting requirement under this subsection shall file its initial report under this subsection for the 4th quarter beginning after the quarter in which the employer becomes subject to the reporting requirement. Once an employer becomes subject to the reporting requirement under this subsection, the employer shall continue to file its quarterly reports under this subsection unless that requirement is waived by the department.