John Quinn, of John M Quinn & Co Solicitors, is seeking to have the statutory instrument introducing the new payment model quashed. The action has been brought against the justice minister, with the Law Society of Ireland named as a notice party.

The new system, which came into force this week, replaces payments based on the number of court appearances with a flat fee of €520 for representing a client in District Court criminal cases.

On Thursday, Mr Justice Anthony Barr granted Mr Quinn permission to bring judicial review proceedings after an ex parte hearing.

Counsel for Mr Quinn, Feichín McDonagh, said the regulations had “upended” the criminal legal aid system, introducing sweeping changes affecting solicitors and the majority of defendants appearing before the District Court.

Granting leave, the judge described the case as one of considerable public interest affecting both solicitors and the operation of the criminal justice system, and said it should be determined as quickly as possible.

In court papers, Mr Quinn says most of his clients cannot afford private legal representation and argues his constitutional right to earn a living depends on the legal aid scheme.

He claims the new regulations are unconstitutional because they provide a single fixed fee regardless of the number of alleged offences or court appearances required. He also argues payment is only made when a case concludes, depriving solicitors of prompt remuneration and, in some circumstances, potentially leaving them unpaid.

Mr Quinn further contends the regulations are “arbitrary, capricious, and unjust” and are incompatible with the Criminal Justice (Legal Aid) Act 1962, which he says provides for legal aid certificates to be granted for individual offences rather than multiple offences under a single payment.

He is also seeking an interim order suspending the regulations.

The case will return to court on Tuesday.