Scottish Natural Heritage has objected to the world class golf course planned for the Coul Links near Embo which opponents say will destroy a unique area of dune land.
It is the latest blow delivered by conservationists who want to stop the proposed development..
SNH has submitted its advice to planning authority Highland Council on the proposed course and said it is objecting despite recognising "the many benefits the development would bring."
"Having considered all aspects, SNH is objecting to the proposal due to the extent of impact on the Loch Fleet Site of Special Scientific Interest (SSSI)," said the Government wildlife agency.
Nick Halfhide, director of operations, added: “We have worked closely with the developer on this proposed new golf course and appreciate the efforts they have made in trying to mitigate the environmental impact.
“We recognise the many benefits the development would bring to Embo and the local economy, and we welcome the developers’ commitment to high standards of construction and management.
“However, we are not able to fully support the development as proposed due to the loss of more than 16 hectares of nationally important sand dunes, and the impact on the special plants and animals found there.”
The development proposals include a range of measures to improve the management of the site for nature but SNH considers these do not outweigh the permanent loss to the sand dunes.
SNH say Coul’s sand dunes contain some of the best dune habitat in Scotland and this is also one of the few sites in Scotland to support populations of green felt lichen and the rare Fonseca’s seed fly.
It is the second major blow to the scheme within days.
Scotland’s largest conservation charity, The National Trust for Scotland, has also submitted a formal objection to the planning application made by Coul Links Limited to build the 18-hole golf course, a clubhouse and associated buildings, as well as an access road on top of the protected sand dune system.
Its objection adds to others concerned at the loss of Coul Links, which they claim would transform an “irreplaceable piece of Scotland’s heritage”.
The trust also questions the economic value claimed for the project, which is being led by Mike Keiser, the American billionaire golf resort developer, and the hotelier Todd Warnock.
The trust’s head of natural heritage policy, Stuart Brooks, said: “The Coul Links are an example of an increasingly rare coastal habitat of international significance. This beautiful and wild place should continue to be protected for the nation.
“While it is perfectly understandable that local people want and need jobs, we know from the Dornoch Area Community Interest Company that it is the area’s outstanding natural environment that is the biggest draw for visitors, and this could and should be a positive foundation for sustainable economic development.”
He added: “The Coul Links and the dune heath sustain a wide variety of internationally important wildlife, including plants, birds and insects.
“They represent an increasingly rare part of Scotland’s natural heritage and it is our obligation as a nation to cherish places like this for the long term in the face of calls for what might well be illusory short-term benefit.”
A spokesman for the developers has said: “Specialists were engaged to develop a golf course that minimises initial impact and that will provide long-term biodiversity gain for this special site.”