Garry Graham, Prospect’s deputy general secretary, said the government can’t be allowed "to pick and choose which parts of an agreement it will honour and to back out of the parts that may not be convenient any longer".
He added: "Years of pay restraint means that our members will already face lower pensions than they might have expected when they come to retire. Now they are being penalised again by the government going back on its agreed terms.
"It is no wonder more and more of them are beginning to wonder if their future might be better outside the civil service."
Paul Nowak, TUC’s deputy general secretary, has a similar position.
He said: "Public sector pension schemes have been cheaper than expected. Under the agreed rules, which the government committed to for 25 years, this should mean lower contributions or improved pensions for members.
"But halting the valuation process leaves this in jeopardy. The government needs to stick to its own rules and deliver what it pledged."