Farmers and landowners opposed to Transpower's plan to build a string of giant pylons from South Waikato into Auckland are planning a campaign of civil disobedience to disrupt the scheme.
And a dissenting member of the Electricity Commission - which approved the plan yesterday - has warned that it could cause widespread blackouts.
South Waikato dairy farmer Christina Baldwin, a member of the New Era Energy farmer lobby group, said landowners had waged war with words and "now we're preparing to wage war with actions".
She had heard rumours of people "renewing gun licences" and stockpiling materials to block farm access for Transpower workers.
The lines would follow only one route and therefore "it won't be very hard to sabotage", Ms Baldwin said.
"I'm absolutely outraged. I'm looking at Mt Maungatautari [an ecological sanctuary] now and the thought of those things [high-tension powerlines] swanning across the countryside makes me sick."
The Electricity Commission finally gave the $683 million project the go-ahead after nearly two years of bitter argument and fiery protests.
Resource consent must now be obtained for the pylons, and landowners opposing the controversial project are vowing they won't give up their fight.
Those in or near the path of the new lines said yesterday that they would make life difficult for Transpower, particularly when it came to accessing land.
The commission's job was to assess the economic questions of whether Transpower is spending its money the best possible way.
Deputy chairman Peter Harris said the proposal from Transpower to put a line of 400 pylons up to 70m high along the landscape was the most cost-effective option for maintaining reliable supply.
"I want to stress that we did not give the proposal an easy ride," Mr Harris said.
The proposal would see new lines put up between Whakamaru near Tokoroa and Otahuhu in South Auckland, with a line upgrade also implemented through to Pakuranga.
The new lines will be capable of carrying 400kV but will initially be operated at 220kV and cranked up at a later date.
Mr Harris said the next-best alternative would have seen a smaller 220kV line built in the first instance and a second line built when the extra electricity was needed.
Transpower's proposal was better than that best alternative "by at least $11 million", Mr Harris said.
He acknowledged the opposition of affected landowners to the project, but emphasised it was not the commission's job to plan the national grid, set radiation exposure limits or look at resource consent issues.
Mr Harris said that despite this, the commission had examined exposure limits and found that the tower design Transpower proposed would mean electric and magnetic exposures were "at least 10 times" lower than the recommended maximum limits laid down by the National Radiation Laboratory.
He said society would always make intrusive provisions whether it be in the form of a road or rail corridor, electricity line, dam, power plant or sewage treatment plant.
"We have to have confidence that the resource consenting process will be responsive to concerns."
But another Electricity Commission member, engineer Graham Pinnell, said the lines could cause widespread blackouts if it failed under high load.
Mr Pinnell said yesterday that the lines would initially carry 220kV from 2011, but when it eventually carried a load of 400kV, the upper North Island would be very dependent on it.
"Widespread blackouts due to voltage collapse and cascade failure" were a distinct possibility in any double-circuit failure under a high load, he warned. "Restoration would take days if the failure was physical damage to the conductors or towers, and hours if caused by trippings such as lightning strike."
Mr Pinnell said putting up 220kV lines would be more economic, but the majority of commission members ruled Transpower's plan to build 70m pylons carrying high-voltage lines from Whakamaru to Auckland was $11 million cheaper than the next-best alternative, lower pylons carrying 220kV lines now, with other lines to be put up later.
Landowner Ros Sellers of Te Miro, near Cambridge, also vented frustration that the Electricity Commission had approved the pylon plan and said Transpower would have a big fight on its hands getting resource consent.
"We will do everything possible to oppose this and will make life very difficult. There will be a civil outcry and there is no way they will be allowed to step foot on our property," she said.
Bob McQueen of the New Era Energy group said the commission's independence had been "corrupted", illustrated by the Government's decision not to renew the contract of former chairman Roy Hemmingway.
Commenting on the farmers' warning of mass disobedience, he said: "I think what [they are] saying accurately reflects the strength of feeling at grassroots level. It is a bit like the people of Iraq not having the power to oppose what the Americans are doing in their country. They are forced to take action themselves."
The Government could yet choose to fast-track the resource consent process by "calling in" the project on the grounds that it is of national significance, a move Environment Minister David Benson-Pope is considering.
Transpower and the Council for Infrastructure Development yesterday welcomed the commission's approval, but Manukau City Mayor Sir Barry Curtis was scathing and promised his council would fight the pylon project during the resource consent process.
"I've been to Japan and seen these things and the effect is absolutely amazing. The people of New Zealand have no idea," Sir Barry said.
"They will destroy the magnificent rural countryside. They are giant War of the Worlds monsters that will stretch from the city and beyond."
Transpower has already purchased some of the land it needs along the pylon route. Yesterday it revealed it has bought 61 properties at a total cost of $119 million.
* Later this year: Possible appeal for judicial review of the decision.
* Public submissions to a board of inquiry if the Government "calls in" the project to avoid lengthy consent hearings.
* Early next year: Design work finalised.
* 2009: Line and pylon construction begins.
* 2012: Line completed and commissioned.