Firefighters in Cumbria will be unable to respond effectively to flood emergencies if planned crew changes are introduced, union bosses claim.
The Fire Brigades Union (FBU) says plans to reduce staffing on sophisticated rescue equipment by eight are "ill thought out".
The union claims reduced crews could mean some equipment being unavailable for use at the same time.
Cumbria Fire and Rescue Service insists it has sufficient staff resources.
The FBU claims the proposals will leave insufficient firefighters to crew the county's Major Rescue Vehicle (MRV) and Aerial Ladder Platforms (ALPs) at the same time.
Each £400,000 ALP needs two specially trained firefighters to operate them.
The MRV turns out to road traffic collisions involving heavy goods vehicles, as well as to water rescues. It carries specialist rescue equipment, including an inflatable boat and outboard engine.
FBU brigade secretary Mally Hind said: "This ill thought out proposal is based purely on cost and not on risk.
"It's not that many weeks ago that new Prime Minister David Cameron said there would be no cuts to front-line services. Yet here we are looking at the loss of eight firefighter posts.
"If this proposal is allowed to go ahead, there will be a detrimental effect on public safety."
Cumbria's chief fire officer Dominic Harrison said any staff reductions would be met by natural wastage and redeployments.
He added that both pieces of equipment were rarely needed at the same time, but that if they were, additional staff resources would be found.