Firefighters in England and Wales are to strike over eight consecutive days in an ongoing row with the government, the Fire Brigades Union (FBU) says.
The latest action, from 9 August, will be held over three hours each day during the eight-day period, it said.
The union has said "unsafe and unrealistic" proposals will see firefighters working longer and having their pensions cut.
But new fire minister, Penny Mordaunt, said strikes were "counterproductive".
The strikes will take place from 9 August until 16 August, between 12:00-14:00 and 22:59-23:59 BST, the union said.
No industrial action would be taken in Scotland and Northern Ireland, where improved pension proposals are being discussed, the union added.
The FBU says union members have already staged walk-outs over 24 days since strikes began in September last year and firefighters have gone on strike for more than 160 hours.
Fitness test fears
The row centres on ministers' plans to raise firefighters' retirement age from 55 to 60 and increase their pension contributions.
The FBU said it feared many members could fail the fitness tests required to remain on active duty in their late 50s, and therefore have to leave the service.
It said proposals would also mean that if firefighters opted for early retirement, the reduction in their pension would be "unacceptably high".
However, the government has said the deal on offer was fair.
FBU general secretary Matt Wrack said it was "absolutely ludicrous that a government can impose a scheme which means that firefighters will have to ride engines and rescue people from fires up to the age of 60".
"This is unsafe and unrealistic for both firefighters and the public.
"We know it, and the public know it, but the government will not listen to the evidence-based case we have made to them," he added.
The union asked for "flexible retirement options" to be included in an improved offer.
However, a Department for Communities and Local Government spokesman said an improved pension offer and "new principles on fitness" had already been offered to union leaders.
The spokesman said Ms Mordaunt, who was appointed fire minister earlier this month, had met with the FBU on 17 July and had offered to work with them to break the deadlock.
The minister had been due to meet with the FBU again next week, it said.
Ms Mordaunt added: "The action by the FBU is completely futile and counterproductive to the interests of their members and the public.
"I hope they will soon realise that and re-engage so we can get this situation swiftly resolved."