Ouano Tante worked the afternoon shift at the Tyson beef plant in Joslin, Illinois, for five years. But when she and hundreds of her co-workers arrived at work on August 13, they found the plant closed. They speculated that someone on the morning shift might have gotten injured. Then two mid-level supervisors came outside in tears. Plant supervisors told workers the plant was closing permanently, effective immediately. Inside, the early-morning shift had just ended when the workers were informed it would be their last. The cafeteria erupted into chaos.
This is definitely illegal and they can take Tyson to court under the WARN Act https://en.wikipedia.org/wiki/Worker_Adjustment_and_Retraining_Notification_Act_of_1988 but Illinois also has a similar law so they could pursue that too.