Developer Paddy McKillen has won a High Court case aimed at widening the grounds upon which he is challenging the National Asset Management Agency.
Mr McKillen is opposing NAMA's decision to acquire €80m worth of loans given to 15 of his companies by Bank of Ireland.
The decision means Mr McKillen's lawyers will be able to argue that NAMA is acting in breach of the European Commission's decision to approve it.
The challenge goes to full hearing in two weeks' time.
Mr McKillen's legal team argued yesterday that the European Commission's decision to approve NAMA obliged the agency to only acquire loans that are impaired. Mr McKillen claims that his loans are not impaired.
His argument was rejected by lawyers on behalf of NAMA and the State. They argued that Mr McKillen's attempt to add to his case was being made too late.
They also argued that the claim being made could not be adjudicated on by an Irish court and that the argument lacked substance because the legislation setting up NAMA states the agency can acquire any loan it designates for purchase.
But today, having considered the arguments overnight, Mr Justice Frank Clarke said he would allow the new argument to be added to Mr McKillen's case.
He said that while it could be argued that the application was being brought late, there were reasons why this was so.
Mr Justice Clarke also said he was entitled to allow a late application where the matter was one of public interest, which he deemed this case to be.
He said it was important that any questions regarding the way in which NAMA operates are resolved as quickly as possible to remove any doubts about how it operates.
The judge also said the State's arguments that the new ground of challenge was without substance or merit would be better considered as part of the full hearing into Mr McKillen's challenge to NAMA.
That hearing will now take begin in two weeks’ time before a three-judge division of the High Court. It is expected to last two weeks.