Members of the Fire Brigades Union have voted in favour of industrial action, in a dispute over pensions which could trigger the first national firefighters' strike in more than a decade.
FBU members in England, Scotland and Wales were balloted, with 78% of them voting in favour. Under government plans, firefighters in England will get their full pension at 60. Changes to pensions in Scotland and Wales have yet to be settled.
The union says many firefighters will not be able to maintain fitness standards into their late 50s and this will endanger the public.
FBU general secretary Matt Wrack said: "We cannot expect large numbers of firefighters in their late-50s to fight fires and rescue families without creating danger to the public and firefighters.
"We have repeatedly raised safety concerns and provided strong evidence to back it up but the government just isn't listening. This result is a clear indication of the anger felt by firefighters. It's still not too late for common sense to prevail if the government are willing to return to the negotiating table. None of us want a strike, but we cannot compromise on public and firefighter safety."
'Creating a smokescreen'
Under the plans, those retiring early at, for example, 55 will lose thousands of pounds a year. The government, however, says the existing arrangements are not affordable.
Fire minister Brandon Lewis said: "This government does not believe that industrial action is necessary. The pension on offer to firefighters is one of the most generous in the public sector.
"The FBU is creating a smokescreen around the issues of fitness and retirement age to justify their behaviour whilst ignoring the facts.
"After two years of discussions and improved terms, firefighters will still get one of the most generous public service pensions available - £26,000 a year, when including the £7,000 state pension.
The union said no strike dates have been set yet but it is understood that any strike has to take place within 28 days of the ballot.
The government has countered by saying all 46 fire and rescue authorities in England have robust contingency plans in place.