The Royal College of Nursing (RCN) has warned that NHS staff have already been ‘very understanding' while their pensions were renegotiated in recent years.
The government has ordered a review of all public sector pensions, with deputy prime minister Nick Clegg calling them ‘unfair' and ‘unaffordable'. The Liberal Democrats campaigned for a review before the general election.
The review will be chaired by former health minister John Hutton, Labour MP for Barrow and Furness in Cumbria until the last election.
The government is due to announce any changes in its emergency budget, which will set out at least £6bn in public spending cuts.
A spokesman for the RCN said: ‘NHS staff have been very understanding of the current situation with pensions, and are already making increased contributions while the taxpayer contribution is capped.'
Unite says there has already been considerable reform to all public sector pensions and that they are now comparable with the private sector.
The majority of public sector pensioners receive less than £5,000 a year, according to Unite's assistant general secretary for the public sector, Gail Cartmail.
‘We are not talking about gold-plated riches here, but modest pensions needed to help loyal public servants in their old age,' she said.
The NHS pension scheme was last revised in 2007 to make new entrants pay higher contributions.
The deal maintained the right to retire at 60 and a final salary pension for existing NHS staff, but contributions increased from 6% to 6.5% of salary for staff earning between £19,166 and £63,416.
New recruits to the NHS now join a pension scheme that offers additional benefits in return for a retirement age of 65.
Dave Prentis, Unison general secretary, said: ‘Only three years ago, public sector pensions went through massive changes to make them sustainable and affordable. Since then, there has been constant sniping and carping by the Tories and Lib Dems about unreformed, gold-plated pensions, quoting grossly misleading figures to create a climate for cuts.
‘We are happy to participate in any review and to give evidence to that review, but the government has a responsibility to make sure that it is independent and not a rubber-stamp for its ideological attacks on public services.'