The North Wales Fire and Rescue Service workforce has shrunk by nearly a fifth since 2010, new figures show.
The Fire Brigades Union said firefighters are being asked to do more with less.
Freedom of information requests by the union 724 people were employed by North Wales Fire and Rescue Service this year, including full-time and on-call fire fighters and other supporting staff, such as call handlers - 159 fewer staff than the workforce of 883 in 2010. It meant the number of jobs fell by 18 per cent.
Of the 49 fire and rescue services to provide data, the number of firefighter jobs has fallen by 21 per cent in the UK over the last 14 years, with Wales losing 500 firefighters.
Matt Wrack, FBU general secretary, said: "Fourteen years of austerity have devastated the fire and rescue service. Every region has been hit, with 12,000 firefighters lost to cuts across the UK."
He added the rise in flooding, wildfires and storms due to the climate emergency, means firefighters are "being asked to do more with less", adding: "999 response times are slower than ever before, putting homes and lives at risk.
"To protect the public, Labour must invest in the fire and rescue service as a matter of urgency."
The figures also show a dozen fire and rescue services in England lost a quarter or more of their workforce. Buckinghamshire saw the biggest fall, with its fire and rescue workforce down 40 per cent from 2010.
The FBU has also found that 4,000 firefighters have both a full time and an on-call contract, meaning they will be counted as two firefighters in the data.
A Home Office spokesperson said: "Throughout the country, our firefighters operate in uniquely challenging and high-risk environments, constantly going above and beyond the call of duty to protect our communities.”
They added: "We will continue to work closely with stakeholders across the sector to ensure all services have the resources they need to protect communities at the highest standard."
Fire and rescue services have received around £2.87 billion this financial year, they said.