Firefighters in several areas of England have backed calls for a ballot on strike action if no agreement over pay and new working conditions can be reached.
Many crews were only answering emergency calls
A number of crews have taken action this week, claiming the pay agreement reached after last year's national strike has not been implemented.
Some firefighters are only dealing with emergency calls while others are working to rule.
A meeting between the Fire Brigades Union (FBU) and service bosses is taking place in Manchester on Thursday to try to resolve the dispute.
Crews at some stations in Cornwall joined the latest action but returned to normal work on Thursday.
Mike Tremellen, local FBU Brigade Chair, said: "The general feeling is one of anger and frustration.
"There is still underlying anger that there is no movement on pay and negotiations although I believe there is a meeting today."
Asked about the possibility of a strike, he said: "It depends on what happens with our pay and negotiations, but there is a recommendation for a ballot for industrial action nationwide at the national conference in June if nothing happens before then."
Steve Ainley, vice-chairman of the FBU in Nottinghamshire where many crews have been answering emergency calls only, said: "Firefighters are absolutely disgusted by the way they have been treated - it is completely unacceptable.
"Everyone in the fire service is affected by this (pay) agreement and nobody has had the increase they were promised, except the chief fire officers.
"As far as I know, all non-999 calls are being referred to the appropriate service - and there has been no failure to respond to any incident that has needed attention (in the East Midlands)."
'Good will gesture'
Another area affected by the protest is Brighton where crews at the three main stations have taken industrial action.
Jim Parrot, of East Sussex FBU, told BBC News Online: "I am very frustrated with our local employers because they could resolve it (the pay dispute) as well.
"None of the them have spoken to the Fire Brigades Union locally. They seem to be hiding behind the national issue."
Meanwhile, in the West Midlands about 300 firefighters were only responding to 999-calls earlier this week.
Union representative Phil Goalby said all crews were working normally again in "a gesture of good will".
Lancashire brigade members are also taking action and Steve Harman, the county's FBU secretary, said: "The members are extremely angry and will only go back if I can explain to them the national picture."
Mr Harman said he expected his members would back national industrial action if a ballot was called.