Around a hundred workers at Ford UK's manufacturing engine plant in Bridgend have gone on a 24-hour strike.
They join employees from five other Ford UK plants who are striking over changes to the company's pension scheme and its plan to introduce lower pay rates for new employees.
Union members had voted to go ahead with strike action in May but postponed announcing the ballot results publicly to allow further negotiations with the company to go ahead.
But the Unite union, who represents around 1,200 Ford staff across the UK, says its members decided to go ahead with the strike after talks collapsed.
In response to the claims by the union Ford responded: