The judge has reserved his decision in an Environment Court hearing to determine whether climate change considerations can be taken into account in granting mining consents.
Buller Coal and Solid Energy have both applied for resource consents to set up new coal mines on the West Coast.
They say the regional authorities making those consenting decisions cannot take into account the effects on climate change of greenhouse gases associated with coal use.
And Solid Energy says the gases are a result of coal combustion, not of the land use applied for in the consent.
But the West Coast Environmental Network says decision makers must be able to consider the contribution that coal burning discharges will have on climate change.
The hearing was held in Christchurch on Tuesday.
The judge has reserved his decision.