Hampshire and Essex-based electronics firm SELEX Galileo says measures have been ongoing for several months to try to cope with a decrease in orders.
But the company said to ensure it remained competitive, it had been forced to announce a planned reduction in the workforce of up to 25 per cent at the Basildon and Portsmouth sites.
The company has begun collective consultation with elected employee representatives.
SELEX Galileo will be making every effort to avoid compulsory redundancies. Should they be necessary, they will not take place prior to March 2013 and outplacement support will be provided. The reduction in workforce will not affect the delivery of any programmes or contracts currently underway."
The company will also hold individual consultations with employees affected. Employees currently on training programmes, such as technical and business apprentices, industrial placements and graduates are not affected by the announcement.