THE Court of Justice of the EU (CJEU) is to be asked to decide issues concerning the extent of Coillte's environmental responsibilities in relation to grid connection works for a windfarm in Co Laois.
The issues concern whether mitigation measures can, as a matter of law, be considered at the screening stage of a particular development, a High Court judge said when he agreed to refer the case.
Their determination will involve considering requirements of the EC Habitats Directive, Mr Justice Max Barret said.
The judge noted it was argued by objectors to the windfarm the possible extinguishment of the Nore Freshwater Pearl Mussel, a species thought to be unique to Ireland and the River Nore region, "may be at stake".
It is difficult to think of an instance where the objectives and provisions of the Habitats Directive "could be more fully engaged, and require more carefully to be observed", than where possible extinguishment of a species may be at stake, he said.
Coillte previously secured permission for 18 wind turbines and associated development on lands at Cullenagh, close to the villages of Timahoe and Ballyroan.
That permission was challenged but was upheld by a 2015 Court of Appeal decision.
People Over Wind and environmentalist Peter Sweetman, who opposed the permission, later challenged a July 2016 determination by Coillte, made under 2011 regulations giving effect to the Habitats Directive, that grid connection works to connect the windfarm to an ESB substation in Portlaoise did not require a stage two appropriate assessment.
They argue such an assessment is required for reasons including the grid connection works, individually or with other plans or projects, are likely to have a significant effect on a European site.
They also claim the mitigation measures proposed were not clearly defined and do not form part of an enforceable development consent.
Coillte argues its determination complies with the Habitats Directive and, given the outcome of a stage one screening assessment, there is no requirement for a stage two assessment.
It also maintains protective measures applied at the design stage of a proposed development can be taken into account in the stage one assessment.
On Friday, Mr Justice Barrett said he considered the CJEU's views on the issues raised were necessary before he could determine the case.