An international panel of experts has asked Scottish ministers to "urgently" call-in a controversial planning decision in the Highlands.
The decision allows for a golf course to be built on a Site of Special Scientific Interest (SSSI).
Highland councillors voted last month to grant permission for the Coul Links course at Embo.
The World Commission on Protected Areas insists the golf course will destroy the integrity of rare coastal habitats.
The Scottish government said it would wait to be officially notified of the planning consent before deciding whether to call it in.
The panel is part of the International Union for Conservation of Nature (IUCN).
About 32 acres (13 ha) of the 18-hole championship course would be built on dunes at Coul Links.
Councillors voted to give the go-ahead to the controversial development despite officials recommending that it be rejected.
A group of conservation organisations, including the Scottish Wildlife Trust, National Trust for Scotland and RSPB Scotland, oppose the project.
In the letter, committee chairwoman Dr Kathy MacKinnon said: "We have reviewed the detailed evidence-based objections by IUCN members the Scottish Wildlife Trust and the RSPB as well as the statutory objection from your own agency, Scottish Natural Heritage.
"As we said in our initial objection to the Highland Council, it is the view of the commission that if consent is given for this development it will destroy the integrity of rare coastal habitats and lead to irreversible biodiversity loss.
"This case is of significant concern to WCPA, particularly as Scotland, through the UK, is a signatory to the Convention on Biological Diversity and the UN Sustainable Development Goals, both of which include commitments on the protection of areas of high biodiversity value.
"The WCPA therefore urges you as Scottish ministers to urgently call in this proposal and defend this internationally-important nature area."
Michael Wong, a North America-based official of the WCPA, said his organisation was urging the Scottish government to protect the Coul Links dunes, associated habitats and rare wildlife.
He said: "If a country such as Scotland is not able to uphold its international commitments, how do we expect other countries to do so."
'Fell in love'
Coul Links developer Todd Warnock said the project involved less than 1% of protected habitat, adding that the course would bring much needed jobs to the area.
He said a management plan would be put in place to improve the land, and deal with invasive plant species that had encroached on the dunes habitat.
Mr Warnock said: "We are ready to start work on the development after three years of scrutiny and having won the support of the local authority and the majority of local people.
"The democratic process has been comprehensive and fair.
"The project has been assessed by the two statutory bodies as well as the competent planning authority and we now look forward to realising the economic benefits such a prestigious golf course can bring to east Sutherland."
Mr Warnock told BBC Radio's Good Morning Scotland programme that he believed that some of those opposed to the project had not even visited the area.
He said: "I have relocated here. I have invested my heart and soul in this area because I fell in love with something around here which is ethereal. It's bigger than all of us.
"But there is no doubt that there is a massive economic challenge here. We could change lives with this project. We can do that and make this environment better."
But Jonathan Hughes from the Scottish Wildlife Trust, who is an IUCN councillor, said: "If an overseas tycoon proposed converting Edinburgh Castle into a shopping centre the Scottish government would quickly step in to protect a national treasure.
"Coul Links is the natural heritage equivalent of the best of our built heritage and Planning Minister Kevin Stewart must surely heed international calls from IUCN's World Commission on Protected Areas to put a halt to this ruinous development."
A Scottish government spokesman said "Councillors have indicated they are minded to grant planning permission, against the advice of Scottish Natural Heritage.
"The local authority must formally notify Scottish ministers of its decision and once that happens, ministers will decide whether or not to call in the application and determine it themselves."