WARN Act
Employers of 100 or more employees must give 60 days’ notice before laying off or terminating 50 or more employees. The 100 employee threshold can be met by:

Employing 100 or more full-time employees; or

Employing 100 or more employees, including part-time, whose combined total hours of work amount to at least 4,000 hours per week, exclusive of overtime.