Up to 500 jobs will be lost at the Atomic Weapons Establishment (AWE), the company has announced.
The jobs will be cut at the Aldermaston and Burghfield sites in Berkshire, according to the Prospect union.
AWE is responsible for making Britain’s Trident nuclear warheads and it also stores nuclear waste from Royal Navy submarines.
The company said it was part of plans focused “on improving and streamlining ways of working”.
As well as the two sites in Berkshire, AWE has facilities in Blacknest, Hampshire, and Coulport in Scotland.
AWE announced the changes to support effectiveness and efficiency of operations in support of its delivery programme.
In a statement, AWE said: “The changes will maintain and enhance the core stockpile, production and capital investment projects with safety, security and quality remaining central to all our operations.
“The organisation is proposing to reduce the number of roles in some support functions and activities of the business where this is appropriate, with a reduction of around 500 roles across the organisation.”