The Government insists there are no plans to abolish the free travel scheme for older people, amid concerns that private operators could withdraw from the scheme.
The Department of Social Protection said it has ordered a review of the scheme following reports that several private operators have abandoned it.
The departures come as companies claim they can no longer afford to carry passengers at the rate paid by the government.
The Minister for Transport, Leo Varadkar, admitted there are difficulties with how the scheme operates at present.
There are, he said, more passes than ever before, with over a million including companion passes. At the same time, the budget has remained static.
He insisted the current review process was about "modernising" the scheme, and any question of abolishing it was not on the agenda.
Kevin Traynor from the Coach Travel and Transport Council of Ireland said his members are "fully supportive of the scheme."
"However, there comes a point where it's not viable to operate a scheme, where you're not getting sufficient revenues to cover your costs," he said.