The SNP's Michael Russell came under fire after new figures showed colleges have at least 21,280 applications on waiting lists.
As The Herald reported yesterday, the figures do not represent the number of individual students involved because it is common to make more than one application. There may also be cases where students have found a place at another college or gone back to school, but remain on a waiting list.
However, colleges, lecturing unions and student leaders all said the figures were evidence of unmet demand and called for places to be expanded.
Now opposition politicians have voiced their concerns over the way the issue is being dealt with by Mr Russell.
Hugh Henry, education spokesman for the Scottish Labour Party, described the figures as "shocking and worrying".
"Mr Russell has not only refused to give a figure on waiting lists, but described the concept as utterly false," he said.
"It's time he fought for proper funding for Scotland's colleges rather than denigrate those who ask legitimate questions."
Liam McArthur, education spokesman for the Scottish Liberal Democrats, said: "The Cabinet Secretary should be careful not to dismiss out of hand these alarming figures.
"While 21,280 applications on waiting lists do not necessarily translate into 21,280 students, it may well be the case that thousands of would-be students are now on waiting lists instead of in the classroom.
"I've become increasingly concerned with the Education Secretary's dismissive approach to challenges facing the further and higher education sectors."
Liz Smith, education spokeswoman for the Scottish Conservatives, added: "Mr Russell bizarrely claims students have never had so many opportunities and he has even challenged the fact that waiting lists exist.
"He needs to wake up to the crisis facing our college sector."
On Thursday, Mr Russell said it was "absolutely wrong" to suggest 21,000 people were on waiting lists who had been denied a place in learning. "No previous government has ever matched our guarantee ... that every 16 to 19-year-old in Scotland not in education, training or a job is guaranteed an offer of a place in education or training," he said. "Some colleges are continuing to advertise course vacancies, meaning that waiting lists for some opportunities are not the way to accurately measure overall demand."
The row follows a survey by Scotland's Colleges of the country's 43 colleges, of which 36 responded.
Subject areas with the highest waiting lists included health care, health and safety, personal care and appearance and engineering.
There is now mounting pressure on Mr Russell to increase the number of student places through additional funding.
The amount of money colleges get for teaching has been cut by nearly 16% between 2010/11 and 2012/13 – from £460 million to £387m.
A Scottish Government spokesman said: "This Government is delivering college courses linked to employer demand and regional needs for our young people, as well as record training opportunities."
He added: "With colleges advertising vacancies, it is clear there are still places available for 2012/13."