Generally, the Worker Adjustment and Retraining Notification Act (WARN Act) is a federal law that requires certain employers to give advance notice of significant layoffs to the employees and others. Layoff notice requirements are intended to protect employees, their families, and communities by giving employees a transition period in which they can adjust to losing their jobs, obtain other work, or pursue training for other work.

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Although the basic idea behind the WARN Act is fairly straightforward, the law is filled with technical requirements which can trip up supervisors and HR specialists. In a nutshell, the WARN Act requires businesses that have at least 100 employees to give 60 days advance notice of any mass layoff or plant closing to affected employees, unions, and local and state governments. To determine how many employees an employer “has” under the WARN Act, it must count all employees at every location, not just the location where employees are being laid off. A number of states also have WARN Act layoff notice laws that may be stricter than the federal law and may apply to smaller employers.

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Layoff notice is required when an employer experiences a “plant closing” or “mass layoff” in which at least 50 employees lose their jobs during a 30-day period. Although part-time employees are not counted in determining whether a reduction in force affects enough employees to trigger the WARN Act, they are entitled to WARN Act notice if they’re being laid off.

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Groups of people entitled to WARN Act layoff notice include employees affected by the reduction in force or representatives of the affected employees, the state’s dislocated worker unit, which responds on-site to assist workers facing job losses, and the local government in which the facility is located.