DETROIT — The United Auto Workers union launched an unexpected strike against Ford Motor at the automaker’s highly profitable SUV and pickup truck plant in Kentucky.

The strike was effective at 6:30 p.m. ET Wednesday at Ford’s Kentucky Truck Plant, where the automaker produces Ford Super Duty pickups as well as the Ford Expedition and the Lincoln Navigator SUVs. The facility employs 8,700 UAW members.

The strike at the plant — Ford’s largest in terms of employment and revenue — marks a major escalation in the UAW’s targeted, or “stand-up,” strikes. It also represents a shift in strategy now in the fourth week of expanded strikes. For previous work strikes, UAW President Shawn Fain has publicly announced the targets before the work stoppages occur.

A Ford source said the union informed the company early Wednesday afternoon that it wanted a new economic counteroffer by 5 p.m. ET, followed by a meeting request for 5:30 p.m. ET with the UAW’s entire Ford bargaining committee, including Fain and union Vice President Chuck Browning.

The source, who agreed to speak on the condition of anonymity because the talks were private, said the meeting lasted less than 10 minutes before Fain declared that the company had “lost Kentucky Truck.”

“The strike was called after Ford refused to make further movement in bargaining,” the union said in a release. “The surprise move marks a new phase in the UAW’s Stand Up Strike.”

A UAW source with knowledge of the talks said Ford did not add any additional cash to its proposed deal, which provoked the strike escalation. The source added the union was expecting Ford to enhance its prior economic offer.

Ford said the “decision by the UAW to call a strike at Ford’s Kentucky Truck Plant is grossly irresponsible but unsurprising given the union leadership’s stated strategy of keeping the Detroit 3 wounded for months through ‘reputational damage’ and ‘industrial chaos.'” 

The latter part of the statement refers to leaked private messages last month in which UAW communications director Jonah Furman discussed the union’s public posturing of issues and targeted strikes as causing “recurring reputations damage and operational chaos” to the automakers.

The companies have argued the messages, as well as the union’s actions, show UAW negotiators were never actually interested in reaching a deal with the Detroit automakers.

“We have been crystal clear, and we have waited long enough, but Ford has not gotten the message,” Fain said in a statement 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.”

Ford said the new strike puts at risk approximately a dozen additional operations at the automaker and “many more supplier operations that together employ well over 100,000 people.”

Ford said it had presented an “outstanding offer” and “has been bargaining in good faith this week on joint venture battery plants,” which have been a recent focus of the talks.

General Motors last week agreed to include workers at its electric vehicle battery plant in the company’s national contract with the union, which Fain called a “transformative win.”

Fain said the union expects Chrysler parent Stellantis and Ford to follow suit, including battery plant workers in eventual contract agreements.

The UAW has been gradually increasing the strikes since the work stoppages began after the sides failed to reach tentative agreements by Sept 14.

The additional workers brings UAW’s total to about 34,000 U.S. workers, or roughly 23% of UAW members covered by the expired contracts with the Detroit automakers, who are currently on strike.

Fain will give bargaining updates and potentially announce further strikes at 10 a.m. Friday online, the union said Wednesday night.