The Tánaiste, Ms Harney, has compared the proposal to reintroduce third-level fees to the ill-fated attempt to introduce property tax in the 1990s, write Denis Staunton in Brussels and Mark Hennessy.
Speaking in Brussels, Ms Harney said it was essential that any measure the Government took to finance the expansion of access to third-level education was practical and fair.
"In the past, we introduced property tax which became a bit of a problem. Even though it affected relatively few people, a lot of people became scared as a result of that and it was a tax that collected very little money. We have to make sure that we don't do that again in this area," she said.
The Tánaiste criticised the Minister for Education, Mr Dempsey, for his failure to discuss the fees proposal in Cabinet before it became public. She said that in a coalition government, neither party could act unilaterally on an issue of such importance.
"It would have been better if we had the discussion internally before we start debating the matter in public. That's not good for the cohesion of the Government. It's not good for the issue itself and it probably leads to a lot of confusion among parents and among students and caused a lot of unnecessary fear and worry."
Ms Harney said she had no knowledge of the proposal before it was reported in The Irish Times this week but added that she had discussed the matter briefly with the Taoiseach during the last two days. She suggested that the issue not only divided the two coalition partners but had created divisions within Fianna Fáil.
"It's no harm that there are differences. That's why we are in different political parties and indeed internally perhaps in Fianna Fáil there's a different approach in relation to this issue as well. Everybody doesn't have the same view. I think it's important that we make it clear what the Government's view is as quickly as possible so that the unnecessary fears and worries that parents and students have are put to rest as quickly as possible," she said.
Meanwhile Fine Gael leader Mr Enda Kenny said Mr Dempsey should "consider his position" .
Ridiculing the Progressive Democrats' stand, Mr Kenny welcomed the junior coalition partners "back from their self-awarded 12-month political vacation since the election last year".
"Now that they are back in the real world, the Progressive Democrats might like to know that college registration fees were increased by 69 per cent in their absence," he said.
"While this explosion of opposition from the PDs is welcome, what universe have they inhabited for the past 12 months when this issue was being widely debated in every newspaper in Ireland?
"The third-level fees plan and higher college registration charges were not included in the Programme for Government, yet the Progressive Democrats were blissfully off the watch when these were being implemented."
The pressure on the Government over education was heightened early this week after Fine Gael secured information under the Freedom of Information Act which showed delays in school building plans.
The disclosure has proven to be a significant morale boost for Fine Gael in the wake of last week's Irish Times/TNS mrbi poll, which showed their support had fallen to just 20 per cent.