The overhaul of the ESA, dubbed the "strategic reform agenda", is aimed partly at reducing duplication in support areas among the four emergency services.

It will mean fire and ambulance deputy chief officers taking on new executive roles that govern areas shared by the Ambulance Service, Fire and Rescue, State Emergency Service, and Rural Fire Service.

Each would report directly to ESA Commissioner Dominic Lane, but would return to an operational role in times of significant emergency.

The United Firefighters Union has written to Emergency Services Minister Joy Burch to protest against the plans.

The union described the structure as "dangerous", saying it was a worrying return to the flawed model of integration and administration identified in the wake of the 2003 bushfires.

"The creation of three executive positions to oversee support services cannot be supported in relation to improved efficiencies and effectiveness; and will not improve emergency service to the people of the ACT," the union wrote.

"The United Firefighters Union implores ACT Police & Emergency Services Minister Joy Burch to provide leadership and halt the return to the dangerous structures and practices currently being hotly pursued by the Justice and Community Services Directorate and the Emergency Services Agency."

The letter also warned such reforms were attempted three years ago but had not worked.

Union ACT branch secretary Paul Swain, also the former territory fire chief, is due to leave the union after a short stint in the role.

He is going to join the Northern Territory fire service as deputy chief officer.

The letter to Ms Burch also denounced changes to the Emergencies Act last year, the "inappropriate" intervention in operational decisions during the Sydney Building fire, and the "continual and systematic" degradation in firefighting numbers.

Mr Lane on Thursday rejected the union's suggestion the overhaul would lead to job losses or that changes to executive roles would create "dangerous structures".

"We've guaranteed under the strategic reform agenda we're not going to lose jobs ... this isn't about job losses, this is about improving service to the community and assuring the community and government we're delivering the best service possible."

He reiterated the agency would retain four integrated operational services, and standards would not drop if executives worked across the services.

"What the government expects is that we operate in a cohesive manner at an operational level, that we collaborate as a management team and that as a unified executive we continue to deliver services.

"That's what we'll continue to do, that's what we've set the agenda around."

He said the agency's executive met members of the Transport Workers Union, the Community and Public Sector Union and the UFU about the proposed restructure last week.

The firefighters union had not raised its concerns with him directly, he said.

"We welcome sitting down with the union and making sure we can work through any particular issues they raise and I would suggest this is the first place to start, rather than penning open letters."

Opposition emergency services spokesman Brendan Smyth urged Ms Burch to support and listen to the territory's firefighters as pressure mounted over her "poor handling" of the agency and restructure.

Mr Smyth said plans to give the deputy chief fire officer more management responsibilities across the ESA were "questionable at best".