For employers with more than 100 employees, you can use the WARN database.
WARN – Worker Adjustment and Retraining Notification
Notices are published 60 calendar days before the effective dates.
It's not 100% foolproof and I question what “effective” means (instant layoffs versus official internal announcement and slower shrinking). It also doesn't cover every instance. I know there might be some companies that adhere by the 60 calendar days and do well to give notice, but some states only enforce the state's Department of Labor to be notified directly; not workers. It's up to them to find that info.
Try it with a search “warn notice [state]” and I'd recommend adding year. My state had an updated pdf, others had dedicated updated web pages.
Never was told this until I looked up if there was a way to get a heads up beforehand, since companies just love springing that up.
Stay safe out there.
Also if anyone has insight in labor law, I'm curious if a company not giving that 60 day notice to workers would expose them to a lawsuit due to this act.