Cornwall Council is being taken to court over plans to build a four-bedroom house on a protected stretch of coastline.
Campaigners claim approval for a two-storey house on Rame Head, which is recognised as an Area of Outstanding Natural Beauty, was a "terrible mistake".
Cornwall councillors approved it despite the authority's planning officer recommending refusal.
Farmer Chris Wilton said: "We’re tenant farmers of the entire area, we farm 280 acres of Rame Peninsula and our family have done so for the past 200 years.
"This piece of land seemed ideal as it is right next to existing cottages and it is well screened, it’s in a natural dip in the landform."
Malcolm Cross, from the Rame Protection Group, objected to the development and now wants Cornwall Council’s decision overturned through the courts.
He said: "It will be a modern intrusion into the landscape and who’s to say that there wouldn’t be other buildings established once the permissions have been granted for one it could be the thin end of the wedge."
Malcolm added all of the expert opinion was against the development, including theArea of Outstanding Natural Beauty planning officer, the principle planning officer for Cornwall Council and around 140 local people.
He said many people were shocked to hear permission had been granted.
The Rame Protection Group is now challenging Cornwall Council’s decision in court on two grounds.
They say reasons were not given for approving the development in an Area of Outstanding Natural Beauty and the council failed to determine whether the development accorded with the development plan.
The date has now been set for a judicial review, which will take place on February 24, 2021.