https://dwd.wisconsin.gov/dislocatedworker/employer/tools/notice/wbcml-overview.htm
Covered employers must provide written notice 60 calendar days in advance of a business closing or mass layoff or reduction in hours.
Employers generally are covered by the WBCML law if they employ 50 or more persons in the State of Wisconsin and Make a reduction in the workforce which affects at least 25% of the workforce or 25 employees, whichever is greater or at least 500 employees.
Two or more groups of employees who are affected during a 90-day period may be considered in aggregate when determining whether the business closing or mass layoff thresholds have been met.