Many less popular Highers could disappear in a major shake-up of the exam system, BBC Scotland has learned.
Almost half of Higher exams face being cut under new plans
The Scottish Executive and the Scottish Qualification Authority (SQA) said they need to rationalise the current exam system with subject cuts a possibility.
Strong educational, cultural or economic cases for courses will have to be made, with geology, cookery, building and politics under threat.
But the executive said it was committed to extending vocational opportunities.
The SQA plan to cull less popular subjects, which it claims cost too much to run, has been approved by ministers.
But a Scottish Executive spokesman denied that up to half of all subjects could be under threat.
He said: "It is sensible to keep the catalogue of subjects fresh and the executive is looking to extend the range of vocational opportunities, not reduce them."
Schools and colleges will receive letters warning them exams are at risk if they attract fewer than 100 candidates a year.
However, ministers have said Gaelic for learners and native speakers is safe. The Gaelic language has been in decline but a bill aimed at protecting it has been put before Holyrood.
The SQA said it was currently developing a policy on low and no-uptake subjects.
Spokesman Mike Haggerty said it would seek to balance choice for candidates with the use of public funding in offering that choice.
But he insisted any decisions would involve a process of consultation.
He added: "Any changes to be made will be as part of a process of improvement and will take a number of years to be implemented."
But he also pointed out that subjects below the 100-candidate low-uptake threshold made up less than 1% of SQA Higher entries in 2003.
Practical courses like Higher professional patisserie and Higher hairdressing are the most likely victims of the rationalisation, which will look at the 79 courses on offer at Higher level.
The news follows last month's announcement by Education Minister Peter Peacock that the Standard Grade could come under threat.
Mr Peacock raised serious questions over its future and proposed a new intermediate exam, which would fall between Standards and Highers.
The idea came on the back of a review of the curriculum which aims to make Scottish education "more attuned" to the needs of children.
BBC Scotland's education correspondent, Seonag Mackinnon, said: "Five years ago the SQA brought in the new Higher Still. It's arguing that it's had five years to bed down and if the exams haven't found a market for themselves then really the prospects are not good.
"What they're about to do is write to schools and colleges with subjects that fall into that bracket and warn them that the subject is under threat and they have the right to appeal against that.
"But I have to say that there is astonishment in many circles that nothing has been known about this plan."
The Principal of Stevenson College in Edinburgh, Susan Bird, said there was a case for reviewing some courses.
She told BBC Radio's Good Morning Scotland programme: "When Higher Still came along the intent was good, but in terms of what has actually happened I think students, as part of an employer market, have voted with their feet.
"They've said that if they want to do building or hairdressing then they should really head towards vocational qualifications recognised by those industries."
However, Brian Boyd, professor of education at the University of Strathclyde, was angry that no widespread consultation had been entered into.
Mr Boyd said: "The argument here is about a slippery slope, if you identify certain subjects as minority subjects, like classical Greek or politics for example, then tomorrow do we identify Latin, do we identify Urdu?
"There needs to be a more rational set of criteria that you apply than simply crude numbers and that's the kind of debate that we haven't had so far."
The Reverend Ewan Aitken, education spokesman for the Convention of Scottish Local Authorities (Cosla), said subjects in the curriculum should meet the needs of a modern society and ensure children remain equipped for the world of work.
He said: "It is not about the removal of subjects or ditching things based on numbers, it is about providing education that is relevant.
"We expect the curriculum review to recommend development of the vocational choices which would be underpinned by a framework of qualifications."
Tory spokesman Lord James Douglas-Hamilton said that the decision should rest with the schools themselves.
"If our head teachers and teachers were put back in charge of the classrooms we could then find out where the demand lies for different subjects and different exams, but for as long as we are stuck with the top-down approach then the kind of problems identified today will not go away," he said.
Scottish National Party spokeswoman Fiona Hyslop claimed that the proposals would lead to a "gerrymandered curriculum".
She said: "Rationing the curriculum will prevent flexibility and choice for pupils.
"This smacks of a shortage of teachers and cost cutting at the SQA rather than a proper curriculum review."