Research by the Complete University Guide says graduate starting salaries in professional posts fell by 11 per cent in real terms, from £24,293 to £21,702, between 2007 and 2012.
That compares with a 4 per cent fall in real terms between 2005 and 2010, the study says.
Those starting jobs in medicine and dentistry - which had the highest starting salaries in 2007 - suffered some of the sharpest falls in income, down by 15 per cent and 9 per cent respectively. Those starting in a career in law received 17 per cent less than they did five years ago, the guide said.
Only two subjects - materials technology and librarianship and information management - registered higher inflation-adjusted pay in 2012.
Dom Anderson, outgoing NUS vice-president for society and citizenship, said graduates are “facing an incredibly bleak labour market”.
“Graduates are queuing up for jobs in an incredibly competitive market, which leaves little incentive for employers to raise their wages,” said Mr Anderson.
The study, which is based on official labour market statistics, also shows the graduate premium – the difference between starting salaries in graduate-level and other employment – had been slightly eroded over the past five years once inflation was taken into account, falling from £6,732 in 2007 to £6,717 in 2012.
Bernard Kingston, the guide’s principal author, said the figures show a “continuing decline in the graduate premium across many subjects”, particularly because they were now required to pay up to £9,000 a year in tuition fees.
“It is helpful for young people considering which subject to choose to see how their earning potential for the occupations for which they may qualify changes over a short time.
“While financial returns should not be the only consideration, they are becoming more important, whether we like it or not. However, with a volatile labour market, it is difficult to predict the future for any particular subject.”
A Department for Business, Innovation and Skills spokesman said: “A degree is still one of the best routes to a good job and a rewarding career.”
Those with a degree earn considerably more over their lifetime, an estimated £165,000 for men and £250,000 for women, he added.