The government remains in dispute with civil servants over redundancy compensation despite reaching an agreement with a number of unions on a new scheme.
The Cabinet Office said the new arrangements will lead to reforms that were fair for civil servants and taxpayers as well as offering “significant extra protection” for lower paid staff.
Five unions - Prospect, the FDA, Prison Officers Association, GMB and Unite - said they will recommend the deal to members.
But the Public and Commercial Services union (PCS), which has already taken legal action over changes to the compensation scheme, said the new scheme was “unacceptable.”
The union’s executive demanded further negotiations with cabinet office minister Francis Maude, warning it will ballot its members to reject the deal if talks were not successful.
The PCS also announced that it will go ahead with a challenge under the Human Rights Act to the current legislative attempts to cut redundancy pay.
General secretary Mark Serwotka, left, said: “We remain committed to reaching an agreement, but we will not be bullied into agreeing massive cuts in redundancy terms simply because the government wants to lay waste to our members’ jobs and livelihoods more cheaply.
“PCS is not just one union out of six. We are the overwhelming voice of civil servants, with twice as many members as the other five unions combined. It is disappointing that the other unions appear willing to accept what is by any measure a severe cut in redundancy rights that effectively tears up the contracts their members have signed.”
The five unions said the new arrangements changed the terms of the scheme to bring them into line with the rest of the public sector, generating more than £1bn of savings and giving special protection to the low paid.