Volunteer firefighters are threatening to quit over claimed flaws in a $20 billion project essential to Australia's energy security.
The Rewiring the Nation plan aims to modernise the electricity grid and connect wind, solar and hydro power to cities and towns.
But southern NSW Rural Fire Service captain Bill Kingwill said he and other volunteers would hang up their helmets if high-capacity transmission lines were built over, rather than under, national parks and farmland.
"It's the danger of it," the Adjungbilly local told AAP on Monday.
"The 500-kilovolt line's potential difference is nearly double that of the 330kV lines, so it will arc a lot further."
That would put firefighters in even more danger, either fighting the fires sparked by arcing or when driving under the lines, the 36-year firefighting veteran said.
Mr Kingwill and other RFS volunteers, including brother Michael Kingwill, drove four hours to Sydney on Monday to deliver to federal Energy Minister Chris Bowen a report casting the massive transmission line HumeLink in a new light.
Grid operator Transgrid has suggested a subterranean HumeLink, to connect Snowy Hydro 2.0 to major lines near Sydney, would cost as much as $17 billion, compared with $4.9 billion for an overhead connection.
But the report by engineering consultancy Amplitude identifies a route that could be built for $5.5 billion and a like-for-like project for the 300km link costing $7.3 billion.
The consultancy said the much higher Transgrid estimates were based mainly on subsea power-cable projects.
Independent Wagga Wagga MP Joe McGirr said the report was a "breakthrough" and showed governments had to seriously consider underground lines across the country.
"This report shows undergrounding transmission isn't just a viable option, it's the best option," he said.
Transgrid said it would review the Amplitude report but remained committed to completing HumeLink by 2026.
"What is not in dispute is the need to deliver the nation-critical transmission project that is urgently required to avoid rolling blackouts and jeopardise the supply of electricity to millions of Australians on the eastern seaboard," a spokeswoman said.
"Delays associated with undergrounding HumeLink will result in a loss of up to $1 billion in lower-cost renewables for consumers."
The construction of overhead transmission lines has been a major flashpoint across the eastern seaboard as the national grid decarbonises and decentralises from a handful of coal-fired power stations.
Tractors and trucks were driven to the front steps of the Victorian parliament in August over concerns about the proposed VNI West line, which is due to connect western Victorian wind farms to southern NSW over mostly privately held land.
