There has been a 27% drop in the number of full-time undergraduate degree courses offered at UK universities over the past six years, data shows.
Research by the University and Colleges Union shows the number of undergraduate courses available has decreased from 70,052 in 2006 to 51,116 in 2012.
UCU general secretary Sally Hunt said there was "less choice" for students.
Dale Bassett, research director of think-tank Reform, said the figures were "misleading".
UCU's analysis of data from the admissions service, Ucas, found course reduction was worst in England, at 31%.
In Scotland, where local students do not pay fees, the reduction was 3%.
Undergraduate courses available in Northern Ireland were down by 24% between 2006 and 2012, and in Wales they were down by 11%.
In England, where tuition fees will rise to a maximum of £9,000 per year from this autumn, the rate of course cutting is varied among the regions, with six of the nine regions experiencing a cut of 25% or more.
The South-West is down down by nearly half (47%), the West Midlands and London both down by a third (33%), but in the East Midlands, courses were axed by just 1.4%.
The report also found that among the single subject courses examined in the UK, science, technology, engineering and maths (Stem) has seen a fall of 14.6%, while social science courses had dropped by 12.8%, and arts and humanities were down by 14%.
'Much less choice'
Ms Hunt said: "Although students in England are expected to pay up to £9,000 a year to study, there is much less choice for them.
"We fear that shifting the burden of funding from the state to the student means nervous universities will look to axe even more courses that they worry won't make a profit."
But Mr Bassett told BBC Radio 4's Today programme: "There are far more people going to university than ever before. There are 100,000 more places every year."
He said: "What we are seeing is choice in action. There are more joint honours degrees, which is what employers want, and more part-time provision."
Ms Hunt disagreed: "There are more students but a reduction in choice. If you are saying that rather than doing a degree in maths or engineering or chemistry you have to do it together than that's a very poor argument."
Commenting on the research, Professor James Ladyman, professor of philosophy at the University of Bristol, said: "I am really concerned that under the new funding environment, universities will look at concentrating their resources on courses which they believe will deliver the highest financial return.
"Provision shouldn't be decided on the basis of short‐term popularity contests, but when you introduce a market that is what happens."
A spokesman for the Department for Business, Innovation and Skills said: "Our reforms are freeing up places at the institutions where students wish to study and bringing higher education into more local communities.
"Student choice is becoming more meaningful and no one should be put off as a result financial concerns."
Official figures from Ucas show the numbers of people applying to university in the UK had been rising - up until this year.
As of January this year, 462,507 UK students had applied for courses beginning this autumn, compared with 506,388 at this point last year, a drop of 8.7%.