They say creating an 18-hole course at Coul Links in Sutherland, near 400-year-old Royal Dornoch, will destroy pristine sand dune habitat and threaten rare species.
Golf impresario Mike Keiser and American entrepreneur Todd Warnock are behind the new course, which will be designed by acclaimed golf course architects Bill Coore and Ben Crenshaw.
It has been estimated it could generate around £7.5 million a year for the local economy and around £14.8m across the Highlands as a whole within the next ten years. It could also support around 250 local jobs and 450 across the region.
Other golf clubs in Sutherland have backed the plans.
But environmentalists fear the project will jeopardise plants and wildlife at Coul Links, which is protected and a designated site of special scientific interest.
Butterfly Conservation Scotland has joined organisations including the Scottish Wildlife Trust (SWT) and RSPB Scotland in opposing the multi-million-pound development.
The group has raised concern over internationally important populations of insects living on the seaside site, including a moth found nowhere else in the UK and the rare Fonseca’s seed-fly.
“Our records indicate that Coul Links is a very special place,” said the charity’s Dr Tom Prescott .
“Turning Coul Links into a golf course would be a tragedy and would permanently damage a place that is home to many rare species.
“I urge the developers to think again. There must be more appropriate locations to develop a golf course than an irreplaceable natural jewel like Coul Links.”
Bruce Wilson, senior policy officer for SWT, added: “It will be almost impossible to construct a golf course on Coul Links without causing unacceptable damage to internationally important sites.”
The developers insist there will be no hotel or residential buildings at the course, stressing that the scheme will be sensitive to nature.
Mr Keiser, who owns Bandon Dunes Golf Resort in Oregon, said: “Our golf course developments aim for minimal intrusion on the landscape and the utmost care and respect for the environment. Our team of environmental advisors is ensuring complete sensitivity to the land, and its location.”
It’s thought a formal application for planning permission will be lodged with Highland Council shortly.