Staff at Vauxhall's car plants in Ellesmere Port and Luton are taking a cut in pay after agreement was reached to reduce their working hours, reported BBC News.
The changes are part of plans by parent company General Motors to cuts costs as it copes with falling sales.
Following talks between company bosses and unions, workers at Ellesmere Port have been told their working week will be reduced from 38 to 30 hours.
The changes have been unanimously accepted by workers.
Workers in Luton will be told on Monday that their hours will be reduced from 37 to 30 per week.
About 2,000 people are employed at the Cheshire plant, which produces the Astra five-door model and the Astra van.
There are about 1,600 staff at Luton, where the Vivaro van is made.
Vauxhall said: "The working time reduction agreements have been reached following extensive talks between senior GM management representatives from across all GM's European Operations and senior Trade Union leaders.
"Dialogue has been constructive and supportive."
The Ellesmere Port factory shut down for a month over Christmas, which the company said was in response to the slump in sales.