The Ministry of Defence is "heading for the cliff edge" and will be forced to axe 3,000 more civilian jobs, according to civil service union Prospect.
In October 2010's strategic defence and security review (SDSR), 25,000 job cuts were announced. But on Thursday Prospect said the figure would reach 28,000, and warned cut backs were being "rushed through" to save money.
"MoD is driving off a cliff, looking over its shoulder at a pack baying for civil service blood. Our members have had enough. Morale could not be lower," National officer Steve Jary said.
"It is cutting the very people it needs to maintain its role as an intelligent customer and to provide support to our hard-pressed armed forces. It just doesn't make sense. The armed forces needs both the skills and specialisms of those in the civil service coupled with the military capacity provided by our soldiers."
Staff affected include engineers, maintenance workers, and admin staff. Prospect estimates there will be 55,000 civilian staff in the MoD by the end of this parliament, compared to 118,000 fifteen years ago.
A MoD spokesman said plans were subject to changes after review: "Each year, we review our plans to take account of changes over the previous 12 months and to ensure that we have the right equipment and manning levels to meet the future needs of our armed forces as agreed in the strategic defence and security review.
"Final decisions have yet to be taken but this annual process rightly considers the status of all our key programmes to ensure the continued coherence and balance of the whole programme."