(Adds BMW response)
LONDON, March 31 (Reuters) - British workers at BMW's Mini and Rolls-Royce car plants have backed strike action over plans by the German automaker to close the firm's final salary pensions, Britain's biggest trade union said on Friday.
The firm wants to close its two final salary pension schemes from June and move all staff to a less generous scheme which new starters have been part of since 2014.
A total of 93 percent of employees who are members of the Unite union and voted in the ballot backed striking and representatives said they would now discuss possible walkout dates involving up to 3,500 workers at four sites.
"BMW needs to reflect on this extraordinary vote in favour of industrial action and the real possibility that its UK workforce will strike for the first time under its ownership in the coming weeks," Unite General Secretary Len McCluskey said.
In Britain, the carmaker builds over 210,000 Minis a year at its central England plant in Oxford, nearly 4,000 luxury Rolls-Royce models at Goodwood in the south and around 200,000 engines at Hams Hall near Birmingham.
The firm said on Friday it wanted to act now to secure the long-term viability of its pensions and remained open to further talks.
"The company has had a number of planned meetings on the proposed changes since the start of the consultation process in September last year, and while it is disappointed by the result of the ballot it remains open to negotiation," a spokeswoman said. (Reporting by Costas Pitas; editing by Stephen Addison)