DETROIT — The United Auto Workers union significantly escalated its strikes against Detroit Three automakers Wednesday by going on strike against a major Ford truck plant in Louisville, Kentucky.

In a surprise move, the 8,700 members left their jobs at about 6:30 p.m. at the plant, which makes profitable heavy-duty F-Series pickups and large SUVs.

UAW President Shawn Fain said in a statement that the union has waited long enough “but Ford hasn’t gotten the message” to bargain for a fair contract.

Ford called the strike expansion “grossly irresponsible” but said it wasn’t surprising given the UAW leadership’s statements that it wanted to keep Detroit automakers hobbled with “industrial chaos.”