Washington, Oct 12 (IANS): The United Auto Workers (UAW) announced an unexpected expansion of its strike to Ford's biggest truck plant in Kentucky as the strike action against the Big Three US automakers continued for the 27th day.

At about 6.35 p.m.on Wednesday evening, the union ordered 8,700 workers to strike at Ford's highly profitable plant in Kentucky where Ford's Super Duty trucks and a pair of large SUVs, the Ford Expedition and the Lincoln Navigator, are produced, Xinhua news agency reported citing local media.

This is the third time the union has escalated the strike against Ford, General Motors and Stellantis and the first time that it has expanded the action without any public warning in advance.

With Wednesday's walkout, which has halted production of lucrative pickup trucks, about a fifth of the auto workers have now downed tools.

In a statement, Ford called the latest move by the UAW "grossly irresponsible".

Ford's Kentucky truck plant generates $25 billion in annual revenue, accounting for a sixth of the company's global car revenue.

The UAW announced a strike at three select factories of Ford, GM, and Stellantis on September 14, after its contract with the Big Three expired.

It extended the strike to 38 GM and Stellantis parts distribution centers around the country on September 22, following a lack of meaningful progress in new contract negotiations.

It called on around 7,000 workers at two more GM and Ford SUV assembly plants to strike on September 29.

In all, about 25,300 out of some 146,000 Big Three automaker workers represented by the UAW are now on strike across the country.