Vauxhall will cut 400 jobs at the firm's Ellesmere Port factory in Cheshire by the end of the year.
The manufacturer, which has made the Astra at the plant since 1979, said it the job losses are linked to "challenging European market conditions and a declining passenger car market".
Vauxhall said a plan has been put in place for a "voluntary separation programme" amounting to around 400 employees by the end of 2017.
Just under 1,800 people currently work at the site, which produces around 680 Astras every day, and the workforce will be briefed on Monday morning.
In a statement, the firm said that cuts were needed to reduce production and improve performance to protect the plant's future.
"The company committed to consult with employee representatives in order to look for potential opportunities to minimise the impact of these proposed headcount reductions. This consultation will take place over a 45-day period in line with legal requirements."