The Government will hear this week if it faces the threat of the first national firefighters' strike for a decade, in a row over pensions.
Members of the Fire Brigades Union have been voting on whether to launch a campaign of industrial action, with the result due at the end of the week.
The union said planned changes were "unaffordable and unworkable", would impose an increase in members' contributions and would put firefighters at greater risk of dismissal without access to a proper pension if they cannot maintain fitness standards as they approach the retirement age of 60.
FBU general secretary Matt Wrack said: "Expecting large numbers of 60-year-olds to fight fires and rescue families is dangerous to the public and to firefighters.
"The Government is simply ignoring the evidence about the physical demands of firefighting and has been unable to answer our concerns during two years of negotiations.
"None of us want a strike, but we cannot compromise on public and firefighter safety. We hope common sense prevails, and the Government returns to the negotiating table."
Fire minister Brandon Lewis said he was "very disappointed" with the ballot, adding that most firefighters will see no change in their pension age.
"Even after the reforms, firefighters on £29,000 will continue to get one of the most generous public service pensions available - £19,000 at age 60 after a full career. That rises to £26,000 with their state pension, the same as the national average wage.
"Someone in the private sector would have to contribute twice as much to get the same pension. The Government's offer still allows firefighters to retire from age 55 with a fair pension - no-one will be forced to work longer and already one in three firefighters has a retirement age of 60."
Military "Green Goddess" machines, used to provide fire cover in previous strikes, are no longer available, but Mr Lewis said local forces are aware that they have to provide statutory levels of cover in the event of a strike.