One in four firefighters may leave their pension scheme if forced to pay higher contributions, resulting in possible funding gap of around £210 million.
Under new government proposals, firefighters belonging to the Firefighters Pension Scheme (FPS) - which sees the Fire Service making employer contributions of 24.4% and closed in 2006 - could be asked to increase their contributions from 11% of their salary to 14%.
But 27% of 8,000 survey respondents told The Fire Brigades Union (FBU) they would leave the scheme if forced to pay more, leaving taxpayers to foot the bill.
The FBU has reacted angrily to the plans. According to the union, not only do firefighters already pay the highest pension contributions in the public sector but the government figures fail to stack up.
The FBU points out that the proposed changes are based on the assumption that only 1% of employees would opt out of the FPS, at a cost of £3.5 million. But if there survey is anything to go by, the sum of lost contributions could be far higher.
FBU general secretary, Matt Wrack, said: "The perverse outcome of the dash for savings to help pay for the budget deficit will be large losses. The viability of the scheme will be badly undermined, costing even more in the long-term.
"It makes no sense for the taxpayer to be paying more, for firefighters to be paying more and the scheme producing less. The Treasury needs to think again and not take a massive gamble with firefighter pensions and taxpayer money."
Earlier this week, government plans to increase the public sector pension age to 66 sparked outcry from unions and strikes by several hundred thousand public sector workers are scheduled for 30 June.