A group of landowners have launched a legal challenge to a new £200m cross-border electricity line being given the green light.
They want the High Court in Belfast to quash the decision to approve the north-south interconnector.
In January the Department for Infrastructure announced it was granting planning permission for the Northern Ireland section of the overhead scheme between Tyrone and Meath.
But up to 6,000 people who own land or live along the proposed route of the pylons and lines are now seeking to have the move judicially reviewed.
Lawyers representing the group Safe Electricity A&T (SEAT) claim the approval should be declared unlawful on conservation grounds.
With no administration currently in place at Stormont, they also contend that the department wrongly gave permission for a development of regional significance in the absence of a minister.
Further areas of challenge relate to the uncertainty around arrangements for reviewing and maintaining the interconnector post-Brexit.
Solicitor Paul Farrell of McIvor Farrell, who is representing SEAT, said: "This is a significant and far-reaching challenge to one of the most extensive planning approvals ever granted in Northern Ireland."
The project to join electricity grids in the two jurisdictions has also 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 an environment reasons - an option dismissed as unfeasible.
Papers lodged in court on behalf of SEAT claim their land will be adversely affected by the proposed development of high-voltage transmission lines.
The overhead cables are in direct opposition to the wishes of landowners and inhabitants, they contend.
The case is expected to be listed for a preliminary hearing before the summer.
