Workers at three BMW plants in the UK are staging a one-day strike in a row over pensions.
The walkout, the first by BMW staff in Britain, is part of a wave of stoppages at the carmaker over the closure of a final-salary pension scheme.
The Unite union, which organised the action that has halted output of the Mini, called the strike a last resort and accused BMW of "pension robbery".
BMW urged the union to return to the negotiating table.
According to Unite, picket lines will be in place for 24 hours at three BMW's plants:
- Cowley in Oxfordshire, where the firm makes the Mini
- Hams Hall in Birmingham, where it makes engines
- And Swindon, where it makes components.
Workers at the Goodwood plant, which makes Rolls-Royce cars, are not walking out on this occasion.
'World class workforce'
The workers are protesting against a plan to close a defined-benefit pension scheme in June and move workers to a contribution-based scheme - something Unite says could cost workers up to £160,000 in lost income.
According to BMW, 67% of those affected by the changes who were eligible to vote backed the action.
Unite general secretary Len McCluskey said: "BMW's refusal to discuss affordable options to keep the pension scheme open means that for the first time, its UK workforce will be taking strike action.
"It is very much the last resort for a world-class workforce that takes great pride in making the iconic Mini and world-renowned Rolls-Royce motor cars and one which could have been avoided if BMW's bosses had been willing to negotiate meaningfully."
BMW said it was "firmly open" to further talks.
"We have been in meaningful discussions with Unite since September of last year and have put forward a number of options to help staff transition to the proposed new pension scheme arrangements," it said.
"Like many businesses, we know that the costs and risks associated with defined-benefit pension schemes makes them unsustainable and unaffordable in the long term."
Unite members are to hold seven further stoppages involving all four of BMW's UK plants at various times. The first of these will happen on 23 April, with the last on 24 May.