Firefighters across Caerphilly County Borough have walked out in the first of three days of strike action.
The walkout is part of a national dispute to protect pensions and protest UK Government plans to raise the retirement age.
Firefighters carried out a series of strikes last year, but action was put on hold while talks were held.
The union argues that firefighters in their late 50s face being sacked or seeing their pension reduced by half because of changes to the retirement age.
Firefighters walked out at noon today and will be on strike until 5pm.
They will also walkout tomorrow between 2pm and 2am and on Sunday between 10am and 3pm.
FBU Wales, Brigade Secretary Cerith Griffiths said this is an escalation in action and firefighters are determined to win the dispute.
Mr Griffiths said: “We are still willing to meet the Government if they will talk to us seriously but firefighters are angry at the proposals and the way the Government has treated them.
“Firefighters are prepared to walk out the door now and stay out if they must as a last resort.”
Matt Wrack, FBU general secretary, said: “After three years of negotiations and an intense four months presenting an indisputable, evidence-based case for the need to ensure a pension scheme that takes into account the unique occupation of firefighting, the government is still burying its head in the sand.
“Several members of government were only too keen to praise firefighters during the winter floods, but their words amount to nothing when they simultaneously ignore issues that threaten the future of firefighters and their families.
“Nevertheless, we remain totally committed to resolving the dispute through negotiation, and are ready to meet to consider a workable proposal as soon as possible.”
South Wales Fire and Rescue Service warned people to be vigilant and sensible during the strike.
Assistant Chief Fire Officer, Rod Hammerton said: “We will not have nearly as many fire engines available and we will have to focus our resources on responding to the most critical incidents where life and property are at threat.
“That means other incidents might get a slower response or less resources. The strike dates coincide with a bank holiday weekend where people tend to make the most of the country side, camping, walking and picnicking.
“During this period we ask our communities to be extra vigilant and remember prevention is far better than response.”