The Public and Commercial Services Union (PCS) has warned the Government that it will vigorously oppose an increase in the compulsory retirement age.
The Government plans to raise the retirement age across the public sector from 60 to 65 and to change the civil service pension from a final salary to a career-average scheme.
The union claims that pushing up the compulsory retirement age will not benefit working people or "create the type of society we want for the future".
The PCS also believes proposals to axe the final salary scheme will cause great uncertainty, suspicion and anxiety among civil servants.
Mark Serwotka, PCS general secretary, said: "These are a complex set of proposals, and over the coming weeks we will be looking at the detail, consulting our members and looking to hold the Government to its promise of meaningful dialogue.
"These proposals have significant implications not only for civil servants, but also for the rest of the public sector," he said. "If good pension schemes are OK for ministers, MPs and judges, then they must be OK for our members and public sector workers."