The United Auto Workers union on Wednesday night called on more than 8,000 workers at Ford’s largest plant to walk off their jobs—surprising company officials who had no warning of the ongoing “stand up” strike’s rapid expansion. 8,700 workers at the Kentucky Truck Plant, which makes Ford F-Series pickup trucks, joined the strike at 6:30 p.m. local time. The action will hobble the facility, which accounts for one-sixth of the company’s total revenue, or $25 billion annually. The UAW has been on strike at all of Detroit’s “Big Three” auto manufacturers, which includes Stellantis and General Motors as well as Ford, for roughly a month. “We have been crystal clear, and we have waited long enough, but Ford has not gotten the message,” UAW President Shawn Fain said Wednesday. “It’s time for a fair contract at Ford and the rest of the Big Three. If they can’t understand that after four weeks, the 8,700 workers shutting down this extremely profitable plant will help them understand it.”