The National Union of Students has no policy on how higher education should be paid for, despite its calls for a return to grants and the abolition of fees in the government's student funding review.
Options such as a graduate tax - one of the possibilities being considered by government - have not been discussed. NUS leaders say they will not make a decision on so-called "middle-ground options" until the government makes clear its intentions.
Owain James, president of the NUS, said: "We are calling for targeted maintenance grants and the abolition of tuition fees."
He said the money the government had made from fees would allow it to implement the NUS's proposals, which were agreed at its last national conference.
But the NUS will remain silent on options such as graduate tax until the government spells out what it wants and how much it will cost. The results of the government's review of student finance are expected in the new year.
Mr James said: "Going to people without the figures is completely redundant and would lead to a pseudo policy. There are hundreds of different options, and we can't do a poll of all of them."
Although many students believe it is through the NUS's efforts that the review has been achieved, some are worried it is going to let the opportunity for change slip through its fingers.
At Sheffield University's students' union, education officer Matthew McGregor said: "The NUS is in a weak bargaining position, (it) should be canvassing opinion and listening to students.
"Conference policy does not deal appropriately with the situation - it asks for a watered-down version of Cubie and the government is offering a little bit more."
Sheffield's union, he said, supported a return to a fully funded system paid for through mainstream taxation.
Other unions are asking students for their views. The University of Bristol's union this week held a referendum on the question "Should this union in principle support the introduction of a graduate tax in return for the re-introduction of universal maintenance grants, and the abolition of tuition fees?" Results are expected today or tomorrow.
Tom Tolliss, education officer at Nottingham University's students' union, said: "The changes that could come through might well put in place the structures whereby top-up fees could actually be implemented in a few years."