The Cowley plant is where BMW manufactures the Mini
Union bosses have expressed concern at the planned weekend closure of the Oxfordshire-based Mini factory.
It is thought to be only the second time in seven years a closure has been made outside of usual holiday periods.
BMW, the company which owns Mini's Cowley plant, denied the closure was due to a fall in production and said it was to adjust shift patterns.
But Unite's Bernard Moss said he was worried about what the closure could mean for the workers' future.
The company has stressed it is not looking to make cuts.
But Mr Moss said all industry was being affected by the credit crunch.
"It would be unique for the Mini to escape what's going on - in that respect it's no surprise.
"There's a global decline in car manufacturing and we're feeling the effects," he said.
Rebecca Baxter, a spokeswoman for Mini, denied the closure was anything to worry about.
"We have already produced and sold more than 184,000 which is actually 12.1% more than last year," she said.
"One of the great strengths of mini production is that we have a really flexible three-shift system and since the very start in 2001 we've adjusted the shift patterns and shift lengths in order to meet the market demand - sometimes week by week."
UK Mini sales have fallen by a fifth on the same time last year, but there has been an increase in US sales.
Less than 35,000 have been sold this year compared with 36,969 in the first nine months of 2007.
BMW forecasts that 237,000 cars will have been produced by the end of the year which is about the same as a last year.