This is a requirement of the WARN (Worker Adjustment and Retraining Notification) Act. A WARN notification is required if more than 500 people (or 33% of the “active workforce”) are being laid off.

这是美国《WARN法案（员工调整和再培训通知法案）》A部分的规定：在超过500人（或33%的‘有效员工’）将被裁员时，企业必须发布WARN通知。

youdao

There isn't a riot act any more, but we continue to use this expression to warn troublesome people to stop being naughty.

虽然现在已没有了取缔闹事法，但人们仍用这个词来警告人群停止闹事。

youdao

New York passed its own WARN Act this past August that takes effect Feb. 1, 2009.

FORBES: Business In The Beltway

So labor advocates are looking to put more teeth in the federal WARN Act early in the next Congress.

FORBES: Layoffs And Lawsuits

Those agreements would supersede any guarantee of notice afforded to them by the WARN Act, says Raisner.

FORBES: Is AOL Skirting Worker-Protection Law With Mass Layoff?