The High Court is to rule on a challenge to promissory notes by United Left TD Joan Collins.
The Dublin politician claims billions of euro of public money has been unlawfully paid out to banks.
Promissory notes were used from 2010 as part of the €31bn recapitalisation of the former Anglo Irish Bank, Irish Nationwide and EBS.
Joan Collins claims the payments issued by the Finance Minister are unlawful because she contends monies were appropriated by him without Dáil approval in a way that could amount to the issuing of a "blank cheque"’.
A senior official at the Department of Finance gave evidence promissory notes are an unusual but not an unlawful instrument and the State argued their use must be seen in the context of the financial crisis.
Because the case raises such important issues about the public purse, three High Court judges heard the challenge and will hand down their ruling later this morning.