Federal WARN Act Triggers: Plant Closings and Mass Layoffs

The federal Worker Adjustment and Retraining Notification Act is triggered by one of two events at a covered employer: a plant closing that causes 50 or more full-time workers to lose their jobs at a single site during any 30-day period, or a mass layoff at a single site that hits either 50 full-time workers who make up at least a third of that site’s full-time workforce, or 500 full-time workers regardless of percentage.¹ When either event is about to happen, the employer owes 60 days of written notice to affected workers, their union if they have one, and state and local officials. The trap in the statute is not the 60-day number, which is simple. It is the counting: who counts as an employee, what counts as a job loss, what counts as a single site, and what window the losses are measured across.

Which Employers Are Covered

Before any trigger analysis matters, the business itself has to be covered. The WARN Act reaches any business enterprise with either 100 or more full-time employees, or 100 or more total employees whose combined weekly hours reach at least 4,000, excluding overtime.¹ The second test is what catches employers who lean on part-time staff. A company with 80 full-time and 25 part-time workers can still be covered if the total weekly hours cross 4,000.

The statute’s phrase “business enterprise” excludes federal, state, and local government employers. Nonprofits that operate as business enterprises are covered. A worker counts as part-time if they average fewer than 20 hours a week, or have been employed fewer than six of the past twelve months.² That distinction runs through every threshold below, because part-time workers are excluded from the headcounts used to measure both plant closings and mass layoffs.

What Counts as an Employment Loss

The trigger counts are counts of “employment losses,” and the statute defines that term to reach further than most people expect. Three situations qualify: an involuntary termination for any reason other than a firing for cause, a quit, or a retirement; a layoff that lasts longer than six months, even if it was announced as temporary; and a reduction of working hours by more than 50 percent during each month of any six-month period.¹

The hours-reduction category is the one employers overlook most often. Cutting an employee from 40 hours to 15 hours a week doesn’t feel like a firing. But if that reduced schedule holds for six months, the law counts it toward the trigger the same as a termination. Keeping people nominally on payroll while giving them almost no work does not sidestep the notice obligation.

Plant Closing Trigger

A plant closing occurs when an employer shuts down a single site of employment, or one or more operating units within a site, and the shutdown produces an employment loss for 50 or more full-time employees during any 30-day period.¹ The shutdown can be permanent or temporary. What matters is that operations at that location or unit actually stop and enough workers lose their jobs because of it.

Part-time employees are excluded from the 50-person count. An employer closing a facility where 48 full-time and 30 part-time workers lose their jobs has not tripped the plant closing threshold. The count is tied strictly to the site or operating unit being shut down, not to the company’s total headcount. Close a single floor of a building that functions as its own operating unit, cost 50 full-time workers their jobs there, and notice is required regardless of how many people work on other floors.

Mass Layoff Trigger

A mass layoff is different from a plant closing because operations continue. The employer cuts staff but the site keeps running. The statute sets two alternative tests, and hitting either one triggers the 60-day notice.¹

The percentage-plus-minimum test: at least 50 full-time employees experience an employment loss at a single site during a 30-day period, and those workers make up at least 33 percent of the full-time workforce at that site.
The raw-number test: at least 500 full-time employees experience an employment loss at a single site during a 30-day period, no matter what percentage of the workforce they represent.

The percentage test is where employers stumble. A site with 150 full-time workers reaches the trigger at exactly 50 losses, because 50 is both the minimum headcount and 33.3 percent of 150. A site with 300 full-time workers has to lose 100 people before crossing the 33 percent line, even though 50 workers have already been cut. At very large facilities, the 500-person test does most of the work: 33 percent of a 3,000-person workforce is 990, which is well past 500.

The 90-Day Aggregation Rule

Employers can’t stay under the thresholds by chopping a single reduction into smaller pieces. If two or more groups of terminations occur at a single site within any 90-day period and none of them individually crosses the 50- or 500-person line, the law adds them together. When the combined total meets a trigger, the employer should have given notice before the first group was let go.³

The only escape from aggregation is proving that each round of losses came from a separate and distinct cause. The burden sits entirely on the employer. Letting 30 people go in January and another 25 in March at the same location will be treated as one 55-person event unless the company can show the two rounds had genuinely unrelated reasons. Vague explanations like “ongoing restructuring” don’t clear that bar.

What Counts as a Single Site of Employment

Every trigger count runs through a “single site of employment,” so how that term is drawn directly changes whether a threshold is hit. A single site can be one building or a group of buildings close enough to function as a campus or industrial park. Buildings that aren’t adjacent can still be one site if they sit in close geographic proximity, serve the same purpose, and share staff and equipment.⁴

Buildings on opposite sides of town with different workers and different functions are separate sites even when the same company owns both. A single office building occupied by 50 different businesses contains 50 separate sites. For workers who travel or have no fixed workplace, the site is whichever office serves as their home base or the location from which their work is assigned.⁴ Foreign worksites are not covered, though U.S. workers stationed abroad still count toward the employer-coverage threshold.

Transfers, Relocations, and Business Sales

Not every job change counts as an employment loss for trigger purposes. When a company relocates or consolidates operations, an employee offered a transfer to a new site within reasonable commuting distance has no employment loss, whether the employee accepts the offer or not. For transfers outside reasonable commuting distance, the employee avoids an employment loss only by accepting within 30 days of the offer or 30 days of the closing, whichever is later.⁵ In either case the offer has to come before the closing, the gap in employment cannot exceed six months, and the new position cannot amount to a constructive discharge.⁶

The statute doesn’t put a specific mileage or minute figure on “reasonable commuting distance,” so disputes over whether a transfer offer actually prevents an employment loss tend to be fact-specific.

When a business is sold, responsibility for WARN notice splits at the closing date. The seller handles notice obligations through the effective date of the sale. The buyer takes over from that date forward. Every full-time employee of the seller as of the sale date is treated as an employee of the buyer immediately afterward, so the buyer’s headcount for any future WARN analysis includes those inherited workers.¹

When the Trigger Is Hit but Notice Can Be Shorter

Three narrow exceptions let a covered employer give less than 60 days of notice after a trigger has been met. The employer bears the burden of proving each one, and even when an exception applies, the employer must still give as much notice as practicable and include a brief explanation of why the timeline was shortened.³

Faltering company. Applies only to plant closings, not mass layoffs. The employer must have been actively seeking capital or business that would have let it avoid or delay the shutdown, and must have reasonably believed in good faith that giving notice would have scared off the financing or deal.⁷
Unforeseeable business circumstances. The closing or layoff must have been caused by conditions not reasonably foreseeable when the 60-day clock would have started, with a triggering event that was sudden, dramatic, and outside the employer’s control.⁸
Natural disaster. No notice is required when the closing or layoff is caused by a natural disaster such as a flood, earthquake, or drought.³

Courts read these exceptions skeptically. A company that watched itself lose money for months and waited until the last minute cannot rely on unforeseeable circumstances. The faltering company exception requires actual evidence of active negotiations, not just a hope that things would turn around.

State Mini-WARN Laws

Federal thresholds aren’t the whole picture. About a dozen states have their own versions of the WARN Act, and several impose stricter requirements. Some lower the employer-coverage threshold to 75 or even 50 employees, reduce the minimum number of affected workers needed to trigger notice, or extend the notice period beyond 60 days. If your company operates in one of these states, both sets of rules apply at the same time, and you must comply with whichever is more protective of workers. A reduction in force that sits safely below the federal triggers can still fire a state obligation, so the state analysis is worth running whenever a layoff is on the table.

1
Office of the Law Revision Counsel. 29 USC 2101 – Definitions; Exclusions From Definition of Loss of Employment
2
U.S. Department of Labor. WARN Advisor – Part-Time Employee
3
Office of the Law Revision Counsel. 29 USC 2102 – Notice Required Before Plant Closings and Mass Layoffs
4
eCFR. 20 CFR 639.3 – Definitions
5
Office of the Law Revision Counsel. 29 US Code 2101 – Definitions; Exclusions From Definition of Loss of Employment
6
U.S. Department of Labor. WARN Advisor – Transfer Offers
7
U.S. Department of Labor. WARN Advisor – Faltering Company
8
U.S. Department of Labor. WARN Advisor – Unforeseeable Business Circumstances