A group of landowners have secured High Court permission to challenge the approval of a new £200m cross-border electricity line.
They were granted leave to seek a judicial review of the decision to give the green light to the north-south interconnector.
A judge held that an arguable case had been established on claims that a senior civil servant wrongly agreed to the scheme in the absence of a minister.
Proceedings have now been put on hold until the Court of Appeal determines the legal power of permanent secretaries to take decisions without a functioning Executive at Stormont.
Up to 6,000 people who own land or live along the proposed route of the pylons and lines are attempting to have the planning permission quashed.
In January the Department for Infrastructure announced it was giving the go-ahead for the Northern Ireland section of the overhead scheme between Tyrone and Meath.
But a group formed under the name Safe Electricity A&T (SEAT) allege the move was unlawful.
Their lawyers contend that a development of such regional significance needed to be signed off by a minister.
In a separate case last month the High Court held that a permanent secretary did not have power to approve a £240m waste incinerator at Mallusk on the outskirts of north Belfast.
That ruling is being appealed in an attempt to clarify the authority of civil servants without a functioning Executive.
However, based on the current legal interpretation, the department accepted SEAT has established an arguable case at this stage on the constitutional point.
Counsel for the department also stressed the urgency surrounding the interconnector scheme, claiming: “The lights could go out in 2021 if this project doesn’t proceed.”
The overall initiative to join electricity grids in the two jurisdictions has also been approved in the Republic of Ireland.
It will involve 85 miles of overhead cables and lead to new pylons being built.
Business chiefs have backed the joint scheme between the System Operator for Northern Ireland (SONI) and EirGrid in Ireland to reduce costs and ensure electricity supplies.
But residents in border areas who objected to the interconnector instead wanted undergound cables for health and environment reasons – an option dismissed as unfeasible.
SEAT’s challenge is centred on approval for more than 100 towers and high-voltage transmission lines.
They also claim the scheme lacks the scientific certainty required under a habitats directive that no harm will be caused to wildlife.
Ruling on the preliminary stage, Mr Justice McCloskey confirmed he was granting leave to seek a judicial review on the ministerial point.
He added that it was “abundantly clear” proceedings should now be stayed until the Mallusk incinerator case is determined.
“The Court of Appeal have given it enormous priority and they are hearing it in a couple of weeks,” he stressed.
“Any stay of these proceedings is going to be a pretty short one.”