Bright senior pupils, whose Higher passes would easily have gained them a university place one or two years ago, face rejection because of an unprecedented clamour for places, heads are warning.
Applications from school-leavers and mature entrants have reached a record high while universities have been instructed by the Education Secretary to tighten up on the number of places they offer.
The news comes on top of figures released last week, showing that further education colleges are turning away at least four times as many applicants as they did last year.
Figures released this week by the admissions service Ucas showed that Scottish applicants to higher education have risen in the past year by 31.2 per cent, by 58 per cent in the "mature" 21-24 age-group, and by a massive 109 per cent for those aged 25 and above. Jobs scarcity for both school-leavers and adults as a result of the recession is being blamed for the increase.
Brian Cooklin, head of Stonelaw High in Rutherglen and a member of the Ucas standing group in Scotland, called on the Scottish Government to fund more student places.
He said recent progress on widening access to students from non- traditional backgrounds could wane and youngsters would be put under stress in the fight for places.
Pupils who would previously have had no difficulty finding a place would struggle - a "grossly unfair" situation, he said, as he accused institutions of "changing the goalposts". Glasgow University, for example, had issued a letter telling pupils that some courses which had required four B passes at Higher now required two As and two Bs.
Mr Cooklin cited the case of one pupil who had applied to a "high tariff" course with five Higher A passes but had been filtered out because she had received a level 2 pass in one of her Standard grades. Faculties of law and medicine were raising the cut-off scores required in pre-entry tests such as the LNAT and UK CAT tests, he added.
Mr Cooklin's advice to schools was: "Ensure that young people are very well informed and make their judgments on good evidence and good information. If they are not able to get into a university course of their choice, there may still be other options via college."
Nevertheless, there was likely to be a cascade effect: although colleges received pound;28 million for expansion last year, there was a danger of a displacement affecting other school leavers, he warned.
The National Union of Students in Scotland and the University and College Union Scotland have urged the Scottish Government to give extra funding to universities so they can boost place numbers.
Universities Scotland, the umbrella body for higher education principals, warned it would damage the quality of education if students were given unfunded places.
In December, under direction from former education secretary Fiona Hyslop, the Scottish Funding Council issued guidance to universities, telling them they must recruit no more than 10 per cent above their target number of students in priority subjects - science, engineering and technology, maths, statistics and operational research (a discipline of maths), computing and information science, and modern languages.
In non-priority subjects, universities must recruit no more than 7 per cent above the number for which they have been funded. At present, there is no limit for priority subjects, but there is a 10 per cent threshold for non-priority subjects.