Representatives of Northern Ireland’s two main unionist parties are to meet the EU’s chief negotiator, Michel Barnier, later to discuss Brexit issues.
The Democratic Unionist Party (DUP) and Ulster Unionists (UUP) are to hold separate meetings in Brussels.
Mr Barnier recently called for “less drama” over the so-called Brexit backstop regarding the Irish border.
The EU negotiator held talks with four of NI’s other parties last Friday.
The backstop is the arrangement which will apply if the Irish border cannot be kept as frictionless as it is now in the context of a wider deal.
The DUP leader, Arlene Foster, has warned that the party will not support a Brexit deal that could lead to any new checks on goods coming into NI from elsewhere in the UK.
Speaking ahead of Tuesday’s meeting, she said: “The United Kingdom single market must be protected with no new borders between Northern Ireland and Great Britain being created. From day one this has been the DUP’s only red line.
She added: “Over 70% of all goods leaving Belfast port are destined for Great Britain. To create a barrier to that trade would be catastrophic.”
UUP leader Robin Swann said it was very important that the voice of unionism be heard in this critical phase of the Brexit negotiations:
“As unionists, it is vital to us that the constitutional integrity of the United Kingdom is preserved throughout this process, but it is also clear that in terms of the economic well-being of Northern Ireland any border along the Irish Sea would be as harmful as a no-deal Brexit.”
Following their meeting with Mr Barnier last week, Sinn Féin and the SDLP said they rejected the possibility of Stormont having a say over what kind of backstop may emerge if there is a ‘no deal’ Brexit,.
Proposals being worked on by the British government are said to include some kind of role for MLAs, but the nationalist parties are fearful that this would give rise to a veto for the DUP.
But Irish taoiseach (prime minister) Leo Varadkar said there is still “a fair bit of work to be done”.
NI secretary Karen Bradley told the Conservative Party conference the government would “never ever allow a border down the Irish Sea”.
The UK is due to leave the EU on 29 March 2019.