A proposed upgrade to a 137-mile power line through the centre of Scotland would break countryside protection guidelines, it has been claimed.
The power line would run from Beauly to Denny
The public inquiry into Scottish and Southern Energy (SSE) plans has begun its final session in Stirling.
The line from the Highlands to Central Scotland would see 600 larger pylons.
Scottish Natural Heritage told the inquiry it breaches encroachment guidelines on the Ochil hills. SSE said it disagreed with SNH's evidence.
The inquiry, which started in Perth in February, was set up after SSE submitted plans to erect new infrastructure of 212ft pylons along the route from Beauly, near Inverness, to Denny.
Those protesting against the plan said it would irrevocably damage Stirling's historic and natural landscape.
The inquiry heard from Gillian Beauchamp, employed on the project by SSE.
She said the landscape and natural beauty of the area around Stirling would not be greatly affected by the upgrade.
However, SNH argued that the larger, heavier pylons along the top of the Ochils to the east of Stirling, go against guidelines set down to protect central Scotland.
SNH's David Cockburn asked Ms Beauchamp: "Do you agree that the guidelines make it clear that the start of these hills needs protection from encroachment?"
Ms Beauchamp pointed out that the upgrade would follow the same line as the current power line and so would encroach no further.
Mr Cockburn said the issue was to stop further development not about the location of the line.
The public inquiry will run until the end of the year
He said: "We are debating whether these guidelines have been complied with or not.
"In no view have these guidelines been complied with."
Ms Beauchamp said she disagreed.
Under the current proposals the new power line would also pass through the site of the Sheriffmuir battlefield.
Four local authorities covering the area where the pylons would be built - Perth and Kinross, Highland, Stirling and Falkirk - have all objected to the plans.
Scottish and Southern Energy said the £320m development was needed in order to meet green energy targets.
The line would allow renewable energy from proposed wind and wave projects in the north to be transmitted to the major population centres of Central Scotland.
The inquiry has been scheduled to end when the Stirling session finishes on 21 December.
A report will be submitted to the Scottish Government in 2008, with ministers then making a final decision.