Some 6000 students at Scottish universities have yet to receive payments for living expenses such as rent and food weeks after the start of term.
The Students Awards Agency for Scotland (SAAS), which distributes the money, defended its role, saying delays only related to late applications for support.
The body has already successfully processed the vast majority of the 150,000 applications it received this year.
However, student leaders have called for an inquiry into why it has taken so long to process applications arriving after the deadline, set for the end of June.
There is also anecdotal evidence that students who applied before the deadline still don't have financial support.
Robin Parker, president of NUS Scotland, said: "The Scottish Government needs to investigate why students will still be waiting for their support payments in November, and look very closely at providing the additional resources SAAS would need to process applications quicker.
"Many students rely on this funding to afford their education, and could struggle to remain at university without this much-needed support."
Stewart Maxwell, an SNP MSP and convener of the Scottish Parliament's education committee, has written to Education Secretary Michael Russell asking him to provide an urgent update on the issue.
Meanwhile, opposition politicians called for the minister to make a statement to Parliament.
Liam McArthur, education spokesman for the Scottish Liberal Democrats, said: "It is inexcusable that thousands of students do not yet have the loans and bursaries they need to pay for food and rent."
Hugh Henry, education spokesman for Scottish Labour, said: "Many students cannot pay their rent or buy their shopping and some are having to put themselves into further debt through more expensive borrowing."
The Scottish Government said it had invested in new technology to make the SAAS system more efficient and believed anyone who applied by the end of June would have received payment.
However, Dominic Smith, a physics student at Glasgow University, disagreed.
"I applied a few weeks after I finished my exams in May. It's almost November but money still isn't through. I'm using a bank overdraft to pay for things like food," he said. "When you phone up you go through this system then get put on hold for what can be up to 40 minutes or not get through at all. I'm even paying for that call with my overdraft."
Craig Angus, vice-president of media and communications at the university's Student Representative Council, said: "It seems to be chaos. We know of 15 students who have been asked to re-send their proof of income because it seems to have been mislaid. We suspect there are many more cases. It is so frustrating because students can't even get through on the phone to find out what is happening."
He added that because applications were stuck in the SAAS system, students often had no proof they have had no payment, so they may struggle to access emergency welfare payouts from universities.
A Government spokesman said: "SAAS is dealing with around 6000 applications received after the deadline of June 30. The vast majority were received in September and October.
"SAAS is committed to ensuring students get the help they need and 100% of applications received before the deadline on June 30 were processed before the student's course began. Even including late applications, over 95% of the 151,000 applications received this academic year have already been processed."
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