The Southampton factory employs 1,100 people
Workers at Southampton's Ford factory are facing a cut in earnings after the firm said it was replacing its two-shift working day with a single shift.
The factory, which makes Transit vans, will also close for 20 days over the next three months.
The announcement on Tuesday came on the day 1,100 staff returned to work after a Christmas break which was extended due to a downturn in vehicle sales.
The company has said there will be no job losses at the plant in Swaythling.
Ford said it was responding to "significantly reduced medium commercial vehicle sales across Europe" and said more than 50% of the plant output's was exported.
The firm said it was aligning shift patterns with required vehicle volumes.
"Production employees will work on this single daytime shift on a rotational basis and will receive full basic pay," it said in a statement.
"Southampton plant is retaining its flexible shift pattern capability during this quarter so that it can respond to any future changes in demand.
"Ford is taking all necessary measures to protect all its plants from creating excess stock and incurring the associated costs."
Reacting to the announcement by Ford, the area's Lib Dem MP Sandra Gidley said the move would amount to a reduction in workers' pay of more than 15%.
"This is a further blow both to the plant and to local workers," she said.
"Unfortunately though, this is not a surprise, as the government has not yet provided the support that Ford bosses and I have been calling for.
"While I welcome the news that no jobs will be sacrificed within the first quarter, and I commend Ford's unwavering commitment to production in Southampton, this constant slide from one desperate measure to the next cannot continue forever."
Mrs Gidley has written to Chancellor Alistair Darling calling for emergency aid for the factory.
The factory had already implemented a four-day week due to "softening market conditions".
Ford plans to halve production of the Transit van at the site over the next three years.
Ian Woodland, from the union Unite, also called for government assistance.
"There's an economic reality, no-one is denying that," he said.
"From the union's point of view we are co-operating fully with management and we hope things pick up again in the future.
"Our workers are suffering financially, lucky though they still have jobs."