Firefighters have demanded that chief officer Lee Howell choose between leading the service in Devon and Somerset and working for the Welsh Government.
The Fire Brigades Union (FBU) is angry at Mr Howell's decision to take on a part-time job as chief fire advisor to the Welsh Government, which began this week, at a time of £5 million cuts to the service and the loss of about 150 jobs.
Officials in the region say the service has been thrown into "chaos" by the corporate plan, which Mr Howell pushed through at a meeting of the fire authority last month.
Members of the fire authority, to whom the service is accountable, but who were not consulted on the part-time job, are seeking clarification of the appointment following claims by the chairman that the extra workload is being done outside normal working hours.
Mark Healey, chairman of the committee, further fuelled the dispute this week, by accusing the union of double standards and pointing out that firefighters could also juggle part-time jobs with their shifts.
Devon and Somerset FBU brigade secretary Trevor French said: "The public and fire crews of Devon and Somerset deserve a full-time fire chief, especially at a time when the service appears to be spiralling out of control.
"For the sake of fire safety here and in Wales, the authority must make sure the service has full-time leadership, particularly in a time of such extensive and dangerous cuts.
"It's time for Mr Howell to choose – either he works to improve the safety of Devon and Somerset, or that of Wales. Doing both is not fair on anyone and cannot be an option."
The job in Wales, one of three national fire advisor roles, along with England and Scotland, was described as a two-day per week "secondment" by the principality, which also said it would pay £44,000 in compensation for Mr Howell's services.
Mr Healey, chairman of the Devon and Somerset Fire and Rescue Authority, told the Western Morning News the job was not "onerous" and would only involve "the odd phone call" during work hours. But the FBU questions whether the £44,000 adequately compensates the service in Devon and Somerset for the loss of the chief, who earned £138,636 in 2011/12.
It also claims Mr Howell has said categorically, including in broadcast interviews which it has recorded, that he will be spending two days each week in Wales.
Asked to clarify the position yesterday, the Welsh Government said the role was two days each week but can be can be "undertaken remotely".
A spokesman said yesterday: "There is flexibility on both sides."
Bob Walker, an FBU official representing the two-county service, said the row came as a lack of full-time workers volunteering for retained stations under plans to scale back six crews, had left the service in "chaos".
The Western Morning News revealed on Monday that some retained pumps had been unavailable for five months last year as managers struggled to recruit part-time crews.
Mr Walker said he had been going "station to station" to address the concerns of members', only a handful of whom had put themselves forward for part-time roles.
"I am out there listening to members who are worried because there does not seem to be any implementation plan," he added.
Brixham councillor Vic Ellery, a new member of the fire authority, said claims that work was being done in Mr Howell's own time were "unbelievably strange".
"We need some sort of report to the next fire authority meeting explaining the facts – at the moment we are reading everything in the Press," he added.
In response to the FBU demands, Mr Healey said the service was in "fine operational shape" despite grant cuts.
"There are a lot of organisations out there that wish they had such commitment from their head of paid service," he added.
"The suggestion that the service is in chaos is ridiculous as is the suggestion that the chief resigns.
"It is important to understand that this commercial arrangement with the Welsh government is consistent with the commercial strategy approved by the authority.
"Last year Lee Howell successfully ran the service and was president of chief fire officers association in tandem.
"Many chief fire officers have additional responsibilities outside of their role in running the fire service and also share responsibilities on a national level. I too have other roles and responsibilities.
"In short what we have here are people trying and working their hardest on behalf and for the public with less funding, instead of throwing rocks, let's all roll our sleeves up for the good of the public."
