Social Protection Minister Joan Burton has confirmed the free travel scheme for pensioners is, like all expenditure, being reviewed for Budget cuts.
More than 1.1 million people avail of the entitlement, either directly, or indirectly through a "companion pass".
The scheme costs an estimated €76m a year.
Minister Burton said that rooting out fraud from the scheme could be one place to start, with nearly 50 passes seized in the last month alone.
"There are requests from a number of operators to have a look at elements of the scheme, because it was felt to be some abuse of the scheme going on by people not entitled to use the scheme, because there may have been people using fraudulent passing and so on, and using passes that they were not entitled to," she said.
"That review is ongoing."