The Public Accounts Committee has asked for a report into why 21 train carriages owned by Iarnród Éireann and worth €44m are not being used.
PAC Chairman John McGuinness has asked the National Transport Authority to report back to the committee.
Speaking on RTÉ's Morning Ireland, Mr McGuinness said this is all happening at a time when Iarnród Éireann was receiving a €36m bailout from the Government.
He said it was clear the company had over-purchased and over-estimated the travelling public.
However, a spokeswoman for Iarnród Éireann has said the surplus train carriages allow for maintenance and additional capacity during busy travel periods.
Jane Cregan said when the carriages were purchased back in 2008 it seemed demand would increase.
She said the economic decline could not have been forecast or that passenger numbers would fall as much as they did.
Mr McGuinness said it is unacceptable that these trains are not being used, and has called for a report into the procurement process and the cost of storage.
He also wants to determine what efforts have been made to lease the carriages.
However, he said there is a "serious problem" in terms of the gauge of the track, as the carriages are only suitable for tracks in Australia, India and Brazil.