The outcome of the first legal challenge to Britain's Brexit vote is set to be heard later today.
The case was brought in Belfast High Court by a cross-community group of politicians and human rights campaigners, who challenged Prime Minister Theresa May's ability to trigger Brexit negotiations.
They want to establish that devolved decision-makers at Stormont Assembly can veto Brexit and hold their own consultation over whether to embark on talks with Europe.
They also aim to protect peace process guarantees enshrined in the Good Friday Agreement which largely ended republican and loyalist violence in 1998.
Northern Ireland shares the UK's only land border with an EU member state, the Republic of Ireland. If the UK leaves the customs union, the EU could demand a secure frontier in Ireland to prevent goods flowing in and out of the EU from Northern Ireland without paying required tariffs or facing checks.
Both British and Irish Governments are keen to ensure there is no return to the hard borders of the past.