Secondary heads have expressed anger and concern that universities are raising their minimum entry requirements to unprecedented levels, potentially excluding pupils from disadvantaged backgrounds.
Brian Cooklin, former president of School Leaders Scotland, said he spoke for a number of colleagues who were "extremely angry" that the goalposts were being moved.
He picked out Glasgow University for particular criticism, saying it had changed its entry requirements mid-cycle last year and then again at the beginning of this year.
"At least this year, Glasgow has issued its statement that it will require four A passes in one sitting for most subjects at the beginning of the cycle," he said. "That is going to exclude a large number of children from being considered by Glasgow. Mr Cooklin is head of Stonelaw High in Rutherglen and a member of the UCAS standing group in Scotland.
But Glasgow University's vice-principal for learning and teaching, Frank Coton, defended his institution's actions, saying he had received very positive feedback from heads. He also denied that Glasgow University had changed its entry requirements mid-cycle at any time.
Glasgow reviewed its entry requirements on an annual basis, but had recently experienced a rise in demand that was above the sector's average, he told The TESS.
Professor Coton commented: "We typically have about 3,500 undergraduate places each year but, as things stand, we have 30,000 applicants for these places at present. That number is considerably higher than it was three years ago.
"What we are doing is setting out to provide a fair and transparent system for potential applicants. We have instituted a system where we are guaranteeing entry to people who reach certain standards.
"That does not mean people who fall below that standard will not be admitted, but we are flagging up at an early stage an entrance level that will guarantee entry. At the same time, we are also drawing the line at the lower end, saying if you fall below this line you won't gain entry to Glasgow - that allows them then to re-target on other universities."
In the past, prospective students for the arts faculty required a minimum of two As and two Bs - now they are guaranteed entry to the newly-named College of Arts with four As; for social sciences, the new requirement is also four As (previously two As and two Bs); for science - three As and one B (previously one A and three Bs).
He attributed Glasgow's rise in applications in part to its higher standing in the National Student Survey, which assesses student satisfaction levels. It ranks third behind Oxford and Cambridge.
Professor Coton said Glasgow had increased its focus on widening access and had a new programme focused on law and medicine.
Both Mr Cooklin and Professor Coton expressed concern that the Browne review of higher education funding and student finance in England would lead to higher fees in English universities and a consequent flood of "fee refugees" over the border to cheaper Scottish universities.
Although an A pass at Advanced Higher now attracts a UCAS tariff of 130 points, an A* pass at A-level has been awarded 150 points. Mr Cooklin is calling for a review of this system, so that an A band 1 pass is treated as the equivalent of an A-level A*.
That would prevent Scottish universities being "swamped" by English applicants, he suggested.
- Original headline: Heads angered by universities raising entry requirements