A council will decide later whether to revoke planning permission for a wind turbine next to a protected neolithic monument in County Down.
Permission for the turbine was granted in 2013 when planning powers lay within the Department of the Environment.
But archaeology experts were not consulted as they should have been.
They say the turbine at Knock Iveagh Cairn outside Rathfriland “will have an adverse visual impact on the integrity of the setting of the monument”.
Work is under way at the site to put up the turbine and the electricity poles needed to connect it to the grid.
The cairn is a 5000-year-old burial site which is protected by law.
It has commanding views of the surrounding countryside.
Since permission was granted, planning responsibilities have passed to councils.
Armagh City Banbridge and Craigavon Council will decide on Monday night whether it should revoke planning permission because the correct consultations were not carried out.
But it is understood councillors have been given legal advice that if they do, they could be liable for the costs of the project.
The bill could be as much as £750,000.
There were no objections as the turbine went through planning back in 2012.
Locals said they only realised it had been passed when a separate broadband mast was erected next to the cairn last month, without planning permission.
Archaeologists in the Historic Environment Division of the Department of Communities were consulted by planners and came out firmly against the mast.
The council will decide on Monday night whether to order its removal.
Arlene Copeland of the Friends of Knock Iveagh group said they were getting lots of “mixed messages” about whose responsibility it was to review the planning decision.
She said they could be left in the “ludicrous” position where one team supervised by archaeologists was on the hilltop dismantling the broadband mast, while another team was there erecting a wind turbine.
On the turbine application, the Department for the Communities said permission appeared to have been granted without “due consideration of the potential effects on the scheduled monument” 100m to the south east.
They said their view that it would have an adverse visual impact should be considered by council planners.
Armagh City Banbridge and Craigavon Council said it was “acutely aware” of the concerns raised.
It said it would give its decision on the turbine and the broadband mast “imminently”.
BBC News NI contacted the landowner, but they did not wish to comment
It is not the first time such a mix-up has led to controversy.
In the mid 2000s, an Early Christian rath, or fortified homestead, in Waringstown, County Down was destroyed during a housing development, after planners first failed to consult archaeologists and later omitted to pass on conditions they had imposed to the builder.
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