FIRE Brigade Employees Union representative Brendan Rea fears it's only a matter of time before a tragedy occurs because fire stations like Fairfield, Cabramatta, Smithfield and Bonnyrigg Heights are "temporarily off line" (TOL) on some days.
The measure is part of state government cost-cutting.
Mr Rea told a Fairfield council meeting that being TOL was a "dangerous" practice.
"It means that on any given day in any suburb of Sydney, residents may not have firefighters," he said.
"There have been plenty of times where our local fire stations have been put temporarily offline, and this does not take into account neighbouring stations in other municipalities like Guildford, Busby and Liverpool, which are all regularly TOL [too]."
But a Fire and Rescue NSW (FRNSW) spokeswoman said stations were only taken offline if the area could be quickly covered by another fire unit.
"Decisions as to whether a fire engine can be taken offline temporarily are only taken after careful consideration of a range of risk factors," she said.
"For example, fire engines are not taken offline under the policy on total fire ban days."
"FRNSW would never put people's lives at risk. In 2012-13 fire engines arrived within 11 minutes at 90 per cent of all incidents.
"In 2011-12, before the policy was introduced, we responded to 90 per cent of all incidents within 11.14 minutes."
Mr Rea said 73 per cent of money being injected into FRNSW was by insurance companies, 14 per cent by the state government and the remaining 11 per cent by local government.
He said Fairfield Council had allocated nearly $1.5 million out of its 2011-12 budget to keep its local stations operating.
"You don't pay for them to be shut or for the crews to be sent somewhere else leaving Fairfield unprotected," he said.
Fairfield Council will write an urgent letter to the NSW Minister for Police and Emergency Services Michael Gallacher, as well as Premier Barry O'Farrell.