Golf tycoon Mike Keiser and his business partner Todd Warnock want to build a new £10m 18-hole course on protected dunes, Coul Links.
The plans were controversially approved by the local council - but then called in for further scrutiny by the government, due to take place next year.
And last week eight animal and nature charities have banded together to create a super-group to oppose the wealthy pair’s plans at the planning inquiry in February.
The charities claim the course - also called Coul Links - would ruin the more than 34 acres of internationally important and irreplaceable dune habitats.
The group’s strongest weapon is the nearly-extinct Fonseca’s seed fly - Scotland’s rarest species which is only found on this short stretch of coast, and nowhere else in the world.
The coalition - which includes Scottish National Heritage, Buglife and Scottish Wildlife Trust - claim fairways and greens would destroy the flies and their habitat.
A spokesperson for Buglife said: “Fonseca’s seed fly is one of the UK’s rarest endemic invertebrates, restricted globally to a short stretch of coast in northern Scotland.
“This species is found at Coul Links within the proposed golf course where its population is perilously small.
“Stabilisation of the dunes and creation of fairways and greens for the proposed golf course will destroy the habitat for the species and further fragment the already fragile population.”
Jonny Hughes, chief executive of the Scottish Wildlife Trust, said: “Coul Links is globally important for nature conservation and because of this it is among one of the most heavily protected areas in Scotland.
“It is alarming that these damaging plans have come so far.
“The Scottish Government’s response to Coul Links is a test of its commitment to caring for our most important habitats.
“Our evidence will demonstrate the immense damage that will be done by carving out a golf course in this truly special place, and we hope it will lead to a swift rejection of the plans by Scottish Ministers.”
Coul Links, near the village of Embo in Sutherland, is a designated a Site of Special Scientific Interest and a Ramsar Site - a wetland of international importance The golf course is the dream of US billionaire Mike Keiser, who owns 11 golf courses and is Donald Trump’s main rival in the luxury golfing market.
His business partner Todd Warnock, who is helping to lead the golf development, is a founding partner at a US healthcare management company.
Both men fell in love with the area when they visited for regular golfing holidays.
They first unveiled their plans in 2015, submitted them to Highland Council in October 2017, and the authority approved them in June 2018.
However, they were ‘called in’ by Scottish Ministers in August due to issues of ‘national importance’.
As a result, the proposals will be heard at a four-week planning inquiry in February where a government planning inspector will determine whether the plans go ahead.
Currently, 2,318 public comments have been registered on Highland Council’s website with 1,861 objecting.
The inquiry will be attended by the Conservation Coalition - a group of charities formed last week to protest the plans.
It includes the Butterfly Conservation Society, Scottish National Heritage, Scottish Wildlife Trust, Marine Conservation Society and National Trust for Scotland, Plantlife Scotland, RSPB Scotland, and Buglife.
Coul Links declined to comment.
But speaking when the plans were unveiled, Mr Warnock said that Coul Links would be a “world class golf course” and attract tourists from across the world.
He added: “The Highlands and East Sutherland area’s are astounding in so many ways.
“Any time I am away, I cannot wait to return. There is a magic to living here.
“It starts for many with the golf but the closer you look, the more you scratch, the more emerges.
“Coul Links is based solely on that notion.
“As an environmentalist myself, it is essential that Coul Links is sympathetically created to strengthen, not weaken, the environmental habitat.”
President Trump owns the Trump Turnberry golf course in Ayrshire and the Trump International Golf Links in Aberdeenshire.