The High Court has granted the Psychiatric Nurses Association leave to challenge new sick pay arrangements introduced by the Government.
The PNA has sought an order quashing the Public Service Management (Sick Leave) Regulations 2014, which effectively halved the entitlement of public servants to paid sick leave.
The union argues that as it is not affiliated to the Irish Congress of Trade Unions, it was not included in negotiations of the new regulations.
It was deprived of an opportunity to explain why the new arrangements should not apply to psychiatric nurses.
In its submission, the PNA argues that no reason has been provided for the exclusion of certain groups such as Central Bank staff from the new rules, while psychiatric nurses who work in situations of "extreme stress and significant hazard" are included.
It argues that the Minister for Public Expenditure and Reform acted outside his powers in interfering with their sick leave, which is a contractual entitlement.
Under the old sick pay scheme, public servants were entitled to up to six months certified sick leave on full pay, followed by six months on half pay over a four-year period.
After that 12-month period of illness, the employee was entitled to the "pension rate of pay" for an unspecified amount of time, subject to the medical certification that he/she would ultimately be able to return to work.
The new regulations challenged by the PNA would reduce those periods to three months on full pay and three months on half pay.
The PNA says that although it subsequently accepted the HRA with the authority of members, the agreement contains no overt particulars or details concerning the modification of their sick leave entitlements.
Mr Justice Michael Peart granted leave to seek judicial review, and the case is now listed for 15 July.
The case has been taken against the Minister for Public Expenditure and Reform, Ireland and the Attorney General.