Ministers have unveiled radical plans to make universities compete for up to a quarter of student places, but concerns were raised that the move will "undermine the quality of higher education".
Under the proposals, around 65,000 places - for students who gain at least two A grades and a B at A-level - will be up for grabs.
And a further 20,000 places will be fought for by universities and colleges that offer "good quality" courses for £7,500 or less.
At the moment, there are about 300,000 student places and each university is allocated a percentage of these every year.
Professor Sir Steve Smith, president of vice-chancellors' group Universities UK, said: "The Government must ensure that the detailed proposals on student number controls do not result in unintended consequences that could be damaging to students and universities' efforts to widen participation" (recruiting poorer students).
"For instance, proposals to create more places for students with at least AAB A-level grades should explicitly allow universities to use contextual data in the admissions process. We must also ensure that by allowing only universities charging average fees of less than £7,500 as part of the 'core and margin' proposals, this does not undermine the quality of the higher education system."
Shadow universities minister Gareth Thomas denounced the move as a "desperate drive to cut fees", and warned it will lead to a "race to the bottom".
Professor Paul Wellings, chair of the 1994 Group of leading universities said: "The Government needs to avoid driving down standards by auctioning students to low cost institutions. Student places must be awarded where there is clear evidence of good value."
The proposals were key measures of today's higher education White Paper, aimed at opening up the sector and giving more power to students.
The reforms are tied to the Government's plans to triple tuition fees to £9,000 from next year.