Volunteer firefighters are threatening to quit their posts 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 could hang up their helmets if high-capacity transmission lines were built over, rather than under, national parks and farmland.
"I don't think politicians or regulators understand just how dangerous these lines become when they are arcing in bad fire conditions," Mr Kingwill said in a statement on Monday.
"I've seen it first hand. It's one flash and you're ash.
"Bad policy just isn't worth dying for."
His comments follow a report released on Monday that suggests there could be almost no extra cost to put one of the largest proposed transmission lines, the 330km HumeLink, underground.
Grid operator Transgrid has suggested a subterranean HumeLink, which will connect Snowy Hydro 2.0 to the NSW southern tablelands, would cost as much as $17b, compared with $4.9b for an overhead connection.
But the report by engineering consultancy Amplitude identifies a route that could be built for $5.5b and a like-for-like project costing $7.3b.
The consultancy said the much higher Transgrid estimates were based mainly on subsea power-cable projects.
"This report makes a complete nonsense of claims that undergrounding is too expensive and will add significant costs to energy consumers," said Michael Katz, a spokesman for community opposition group Stop, Rethink HumeLink.
"What isn't in dispute is that the overhead proposal will rip through habitats of endangered species, increase bushfire risks and jeopardise lives and local industries."
Mr Kingwill and one of the report's co-authors will deliver a copy to the office of federal Energy Minister Chris Bowen on Monday.
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.
Australian Associated Press
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