A no-deal Brexit will plunge Northern Ireland into turmoil, the High Court in Belfast has heard.
Counsel for victims campaigner Raymond McCord claimed the region would suffer worst from the UK quitting the EU without an agreement as he advanced attempts to stop Boris Johnson suspending parliament.
He is seeking an urgent injunction aimed at forcing the British Prime Minister to reverse plans to prorogue the House of Commons ahead of the October 31 leave date.
His barrister, Ronan Lavery QC, argued: "In many ways there are stronger reasons in Northern Ireland why interim relief is applicable, because of the obvious turmoil that will be created here if there's a no-deal Brexit."
With the legal action adjourned to next week, Mr McCord confirmed he still intends to press for an interim order to block the planned parliamentary shutdown.
The Belfast man, whose son Raymond Jr was murdered by loyalist paramilitaries in 1997, is mounting a wider action against any withdrawal from the EU without an agreement.
He claims a departure on those terms would breach the Good Friday Agreement and threaten the Northern Ireland peace process.
Outside court Mr McCord explained why he believes Mr Johnson's prorogation move must be overturned.
"It's undemocratic; we have got a Prime Minister who wants to force Brexit through with no deal," he claimed.
"He also has decided, to help him do that, to bring in a scheme or system of his own way of suspending parliament.
"This is a Prime Minister who will do anything to get his own way, without concern for the people of Northern Ireland or the peace process."
With Mr Johnson pledging that the UK will leave the EU on October 31 "do or die", he is facing three court challenges in England, Scotland and Northern Ireland.
Although Mr McCord's case is listed for full hearing next month, he took urgent legal steps after plans to close parliament for up to five weeks were announced.
His lawyers contend that the use of prorogation is unconstitutional.
At Friday's hearing Mr Lavery told the Lord Chief Justice, Sir Declan Morgan: "Our position is that parliament should have as much time as possible to debate this.
"It may impede it to such an extent that it's not possible to have a proper, effective debate."
Tony McGleenan QC, representing the Government and Prime Minister, pointed out that a similar attempt to secure an injunction was refused in the Scottish case.
Opposing the bid for an urgent hearing ahead of the full judicial review application, he said: "I do not see Northern Ireland-specific aspects for interim relief articulated here."
Adjourning proceedings until next week, Sir Declan imposed a deadline for lodging further papers.