The government is redirecting funding away from students who want to study for a second degree, to prioritise first-time undergraduates.
Ministers say employers should pay more for re-skilling
The Universities Secretary, John Denham, has told England's funding council to switch £100m a year.
It will affect people who want to study for a second qualification at the same or a lower level as they have already.
Learners' representatives said the move made sense but might underestimate the way people need to seek new skills.
It would also affect someone adding a shorter qualification to their existing skills.
In a letter to the Higher Education Funding Council for England (Hefce), Mr Denham took all this into account.
He wrote: "While there may be much benefit to an individual, or their employer, in them retraining for a second qualification at the same level, this is not, in my view, usually as high a priority for public funding as support for students who are either entering higher education for the first time, or progressing to higher qualifications.
"In many cases, it may be appropriate for the employer to pay at least a proportion of the costs of such re-training."
The Department for Innovation, Universities and Skills denied that the move represented a cut in overall funding from September next year.
"Instead the grant will be re-directed to support more people of all ages going to study higher education in England for the first time," it told students.
The president of the NUS, Gemma Tumelty, said the higher education sector would need to consider carefully the balance between bringing more people into higher education for the first time, and the capacity to respond to the rapidly changing skills needs in the workforce.
"We live in an era of serial careers, particularly amongst highly skilled workers, and it would be a great shame if a change in funding arrangements were to limit the potential of those who have found a new direction, and wanted to support this by returning to higher education," she said.
Alastair Thomson, senior policy officer at the National Institute of Adult Continuing Education, said it made sense to stop some people getting repeated public subsidies while others were never given the opportunity, as did the wish to make employers pay a fair share.
But the situation might not be as straightforward as Mr Denham thought.
"It is a complex area, however, people do make false starts in life and may need supported second chances.
"It is unclear, for example, how plans would leave indebted modern language graduates in need of vocationally specific top-up training.
"Similarly, there will be a strong case for continuing, affordable, higher education for retired people who might need to return to the labour market and for public support to combat skills decay and obsolescence in fast-moving technologies."