The Fonseca seed fly is only found on the sand dunes at Coul near Embo, Dornoch, which US entrepreneurs want to turn into an 805-acre, 18-hole course.
The developers promise that the venture will bring new jobs and an influx of tourists to the stretch of coastline.
But conservationists are demanding a study of the Fonseca seed fly and if that shows their habitat could be threatened, the ambitious golf plans could be scrapped.
An online petition to protect the fly has already attracted 500 signatures.
Craig Macadam, conservation director at Buglife, said the rare fly is restricted - globally - to a stretch of Sutherland coastline encompassing the size of around 100 football pitches.
“It’s an endemic species, extremely vulnerable to extinction,” he said.
“Recent survey work by Scottish Natural Heritage found that populations had dropped significantly since the 1970s.
“Its habitat should not be put under threat from yet another golf development.”
An SNH survey, completed in 2013, declares that the fly should be “one of Scotland’s biodiversity priorities”
It adds that the fly is “particularly susceptible to extinction” and is subject to “random demographic fluctuations”.
The site, which borders the North Sea and Loch Fleet, is in a special protected area and has designated sites of scientific interest.
Petitions have been launched both for and against the proposal, with some locals concerned that their views won’t be taken into account.
There was support for the project at two recent public consultations, with exhibitions of the proposals showcased in both Dornoch and nearby Embo.
But one Embo resident, Gillian Emerick, has registered her opposition and claims that many locals are unhappy with the idea.
She said: “There was a bunch of people before the meetings saying it was absolutely marvellous and that there was no point objecting to it because it would go through anyway.”
A spokesman for real estate agents Jones Lang Lasalle said: “The applicant is currently undertaking an environmental assessment of the site and its surroundings with the objective of achieving a development proposal that responds appropriately to the environment.”
The course proposal is being co-led by developer Mike Keiser for Bandon Dunes Golf Resort, a golfing venue in Oregon, USA.
He has been working alongside Chicago-based Todd Warnock, who has already invested hundreds of thousands of pounds in Dornoch in the Links House boutique hotel and the Carnegie Courthouse.
Sutherland councillor Graham Phillips said: “I can’t comment on any active planning application beyond the council chamber for risk of pre-judging it, but the concept of a golf development in the area is interesting and attractive.
“It would offer significant financial benefits to the area, especially if taken in conjunction with proposals to develop the Dornoch airstrip into a more viable operation.”
A spokesman for SNH said: “We’ve advised that surveys be carried out as part of the environmental impact assessment.”
Craig Macadam added: “Scotland has an international responsibility for this species.
“Its habitat should be protected and enhanced, not put under threat from yet another golf course development.”