Leading universities have criticised plans being considered by Labour to cut tuition fees as "implausible".
The party is yet to unveil its policy but Ed Miliband has said he wants to reduce the cap from £9,000 to £6,000.
In a letter to the Times from Universities UK, vice-chancellors in England said this would create a £10bn hole in revenues over five years.
Shadow universities minister Liam Byrne said "the student finance system is going bust" under the current system.
'Barrier to growth'
The vice-chancellors warned that if a Labour government reduced the fees cap, that would lead to "cuts to universities that would damage the economy, affect the quality of students' education, and set back work on widening access to higher education".
In the letter by Sir Christopher Snowden, vice-chancellor of the University of Surrey, and signed by English members of the Universities UK board, it is argued that the move "risks the equality of education for all".
It reads: "Any move to limit the number of students attending universities as a way of reducing costs would remove opportunities for young people and those seeking to return to education, and act as a barrier to economic growth."
They argue that students, especially those from poor backgrounds, would be better helped with greater financial support for living costs from the government - especially as loan repayments only start once a student is earning £21,000 a year.
Sir Christopher later added that Labour had "missed the point", saying: "This is purely a pragmatic issue, that a policy is evolving on the hoof which is not really a practical policy going forward and the potential damage is colossal."
BBC assistant political editor Norman Smith said Universities UK was concerned that lowering fees would leave them more dependent on government funding - and vulnerable to spending cuts.
He said: "But they also question how a Labour government would be able to find the necessary £10 billion over the next parliament to pay for such a cut in fees.
"A task which Ed Miliband has asked the shadow chancellor Ed Balls to resolve - so far without success."
He added: "The intervention of the universities can only add to Labour's difficulties over tuition fees - with some predicting the party could opt to delay any final decision by opting for a review into the future of university funding after the election."
Shadow universities minister Liam Byrne said: "The Tory-led government trebled fees and now it is crystal clear that the student finance system is going bust, saddling students with debts most will never repay of £43,500 on average and costing the taxpayer more than the system it replaced.
"According to new Ucas analysis, trebled fees have deterred thousands of potential students from applying."
He did not confirm the new policy however, saying Labour's plans would be announced "in due course ahead of the general election".