Federated Farmers says Transpower is seeking to take away landowners' property rights over thousands of hectares of land.
The Government's National Policy Statement calls for increases in buffer zones around high voltage lines, although it doesn't specify how much of an increase.
Transpower has suggested 32 metres either side would comply, and help better safeguard the national electricity supply.
Federated Farmers says this would mean that, over the whole country, up to 42,000 hectares of land would be nationalised.
Spokesperson Willy Leferink says the increase from the present 12-metre strip would take away property rights, and require landowners to get permits to carry out work on their own land.
Transpower spokesperson Rebecca Wilson says the increased zones are needed to provide better security for the country's electricity network.
She says all normal farming activity such as grazing and some fencing will continue and only big initiatives, like building directly under a transmission line, will be prevented.
Ms Wilson says it is up to councils to decide on the size of the zone, though Transpower did appeal against the Western Bay of Plenty's district plan when it intended to have a corridor smaller than 32 metres either side of lines.
The issue was resolved by agreement between the parties that the buffer zone would be looked at as part of a plan change now underway.
Steve Hill of Western Bay of Plenty District Council says it has now put out a proposal based on Transpower's recommendated corridor width.
Mr Hill says the council is also an affected landowner, and has put in a submission opposing the proposal, so the plan change is now being heard by an independent commissioner.
Waimate District Council is is also looking at including the new requirements in its district plan.
Resource planner Kevin Tiffen says the council is looking at bringing in different requirements for different voltage lines.
He says Transpower would prefer a uniform 32-metre buffer, but this is being opposed by the local Federated Farmers.