Thousands of students in Scotland have been sent an unexpected bill telling them to pay off their £2,289 graduate endowment immediately.
The fee is being scrapped by the Scottish Government.
Some 3,000 postgraduate students were previously told they could pay off the endowment after their courses ended.
However, the government said because the fee was going all outstanding debts were being collected by the Students Awards Agency for Scotland (SAAS).
Student leaders have warned the measure could lead to an increase, rather than reduction, in debt, and have called on Education Secretary Fiona Hyslop to intervene.
James Alexander, president of the National Union of Students Scotland, said: "Obviously the abolition of the endowment has been a good thing - we were pleased to see that happen.
"But we are extremely disappointed that a previously positive benefit for postgraduate students appears to have been removed with the introduction of this legislation.
"This is affecting a small group of people but an important group of people."
Labour's higher education spokeswoman Claire Baker said the move "really reveals the SNP's attitude towards students in Scotland".
She said: "To call in almost £5m from some of our most talented students just because of petty bureaucracy, without any real warning, beggars belief.
"The deferment to pay the graduate endowment was offered to students by the previous government to encourage them to carry on their studies as far as they could.
"By demanding full payment immediately, in some kind of final demand, the SNP have pulled the rug from under thousands of students who had budgeted to pay this many years down the line."
Liberal Democrat chief whip Robert Brown said: "We voted for the abolition of the Graduate Endowment because we wanted to see increased access to higher education.
"The minister should step in and ask the awards agency to suspend its attempt at immediate collection of this money from post-graduate students. The current situation is ridiculous."
At the beginning of this year, MSPs voted by 67 to 61 in favour of abolishing the one-off charge.
The move meant current students would not have to pay the fee.
A government spokesman said: "Some students who completed their undergraduate courses in 2005, 2006 and 2007 and have continued their studies to a postgraduate level were allowed to defer the payment of the graduate endowment fee until they completed the course.
"This was a goodwill gesture and did not affect the date of liability.
"Now that the graduate endowment fee has been abolished and the scheme is being wound up, SAAS are no longer in a position to allow these students to defer."