Judgment has been reserved in a legal bid to halt the construction of gas storage caverns under Larne Lough.
Campaigners opposed to the plans approved by former Agriculture, Environment and Rural Affairs (DAERA) minister Ewin Poots claim they are so significant and controversial that they should have been referred to the full Stormont executive.
But lawyers for the department insisted he had legal authority to act unilaterally as a matter of political judgment.
Sitting in the Court of Appeal, Lady Chief Justice Dame Siobhan Keegan indicated a ruling will be given in due course.
In 2021 Mr Poots gave consent for the development by Islandmagee Energy Ltd.
It involves carving seven large underground caverns at a depth 1,350m below sea level by a process known as solution mining.
Located within special protection and conservation areas, the project is expected to last for 40 years.
The units would then be decommissioned at the end of their lifespan.
Local campaign group, No Gas Caverns and Friends of the Earth Northern Ireland, have brought a legal challenge aimed at having the marine licence permit quashed.
They claim it will keep Northern Ireland locked into fossil fuel dependency for decades beyond a target set to achieve net-zero emissions by 2050.
The excavation process will also allegedly lead to hypersaline salt and chemical solution being discharged into the sea near Islandmagee, creating a “dead zone” threat to marine life.
Campaigners contended that Mr Poots failed to properly consider the environmental implications of a development proposal so significant, strategic, cross-cutting and controversial that he was required to refer it to the Executive Committee before granting permission.
In August last year their initial application for a judicial review was dismissed at the High Court.
A judge backed the department’s case that amendments in the Executive Committee (Functions) Act (Northern Ireland) 2020 provided more scope for Mr Poots to give the go-ahead without seeking consent from the wider power-sharing cabinet.
Appealing that ruling, the campaigners argued there was a statutory requirement to comply with the ministerial code and refer such a contentious planning decision to the executive.
However, counsel for the department insisted the case had been wrongly depicted.
He told the three appeal judges that Mr Poots’ decision had been stripped of all context and political judgment, in an attempt to portray the case as “hard-edged questions for public law determination”.
Despite opposition from climate change pressure groups, the court was told that a policy on gas storage caverns has been settled at a UK level since 2011.
Counsel also said all environmental grounds of challenge had been abandoned, and claimed an “arid legal question” was being used to take the case through the court hierarchy.
None of Mr Poots’ cabinet colleagues voiced concerns at the time that the planning decision was significant or controversial, the court heard.
Following extensive legal arguments, both sides must now wait for judicial determination on the merits of the challenge.