Production of the Mini at Cowley has been halted because of a 24-hour strike by BMW workers in a dispute over pensions.
Mini and BMW engine production at Hams Hall in the West Midlands and the building of parts for the Mini at Swindon have also stopped for the day.
The walkout is the first in a series of eight 24 stoppages by members of Unite hitting BMW’s UK plants over the next five weeks, including the Rolls-Royce site in Goodwood, where workers plan to take action for the first time on May 5.
Picket lines were mounted at the plants affected by Wednesday’s industrial action.
Unite assistant general secretary Tony Burke said: “Today’s solidly-supported strike should serve as a wake-up call to BMW’s bosses and underlines the determination of Unite members to defend their hard-earned pensions.
“BMW workers are deeply alarmed by the company’s plans which could see some of them lose up to £160,000 in retirement income.
“BMW bosses need to get their heads out of the sand and recognise this is no way to treat a workforce, which has helped deliver record profits and record sales of the Mini and Rolls-Royce motor cars.
“We would urge BMW’s bosses to listen to its world-class workforce, drop its deadline for the pension scheme’s closure and negotiate a settlement which is for the business and the workforce.
“Otherwise the alternative will be more industrial action over the coming weeks and continuing disruption to production.”