The Government has given a "blank cheque" to the children's hospital which risks seeing the project's "monopoly money" spending surge past €2bn, TDs have warned.
Members of the Dáil's public accounts committee made the claim after the national paediatric hospital development board confirmed the exact cost of the project will be unknown until it is completed.
As revealed on Wednesday night by the Irish Examiner, in a letter to the PAC released this week NPHDB chief officer David Gunning said the project's construction spending has risen from €314m in March to €397m by the end of August.
While acknowledging the costs Mr Gunning said they "are within the budget approved by the Government in December 2018", before adding in a separate part of the letter:
"There are a number of exceptions that have always been outside of the approved budget, and for which there cannot be price certainty at this point or for the duration of the project."
Hitting out at the situation at Thursday's PAC meeting, a number of TDs said the lack of clarity on the exact costs is not acceptable and must be immediately addressed.
Labelling the problem as amounting to "a blank cheque" for the project, Fianna Fáil TD Marc Mac Sharry said:
"We're continuing down an endless road in terms of the costs of this project. They got it wrong from the beginning. God knows where it is going to end up.
Social Democrats co-leader Catherine Murphy was similarly critical, saying the costs involved "is not monopoly money" and warning "there is a degree of spin around this because we're hearing that no other projects will be impacted".
The concern was shared by unaligned Independent TD Catherine Connolly and Fianna Fáil TD and PAC chair Sean Fleming, who both noted the NPHDB is attending a committee meeting in the coming weeks.
However, urging the Government to immediately clarify the likely final price of the project, Labour's health spokesperson Alan Kelly warned:
"It is very convenient for the Government this cannot be costed ongoingly and that costs will only be revealed when the whole thing is completed in the years to come.
"That cannot be allowed to happen, the public has a right to know all the costs related to this."