A victims' campaigner who challenged Brexit in the Supreme Court has called on the DUP to support the wishes of the majority in Northern Ireland to remain in the EU.
Raymond McCord, a campaigner for victims of paramilitary violence, said he was encouraged by the ruling that Parliament must vote on whether the Government can start the Brexit process.
But he said he was concerned that DUP MPs would "put party first and people second".
"Because 56% voted in Northern Ireland in favour of remaining within the EU, the DUP should vote for what the majority want.
"I am saying to the DUP now, are you going to go in there and vote for the wishes of the people or will you vote party first and people second?"
DUP MP Sammy Wilson said: "We will be using our votes and voice to ensure a rapid commencement on the negotiations to leave the EU, completely as the Prime Minister promised."
He said the party will ensure "that the issues most concerning to Northern Ireland are articulated by our MPs".
Mr Wilson added: "It would have been totally irrational to have the Northern Ireland Assembly, Welsh Assembly and Scottish Parliament dictate the direction in which the nation should go after such a clear and decisive vote.
DUP parliamentary leader Nigel Dodds said: "The DUP campaigned for Brexit and we believe we are stronger outside the shackles of the European Union. We voted as a whole to leave the EU and that vote must be continually respected."
Sinn Fein's Gerry Adams warned that Brexit "will undermine the institutional, constitutional and legal integrity of the Good Friday Agreement".
He said: "It puts the British Government on a collision course with the EU in which our stability and economic progress are regarded as collateral damage.
"The Taoiseach and the Irish government must uphold the Remain vote in the North. And to argue for the North to be accorded a special designated status within the EU."
SDLP leader Colum Eastwood said the judgment "significantly undermines the value placed on the democratic mandate of our Assembly".
He added: "Northern Ireland voted to remain in the European Union, yet the Northern Ireland Assembly is being denied any role or rights in the upcoming negotiations with the European Union.
"The SDLP is now the only party standing by the will of the majority of people in Northern Ireland at Westminster. We will be the only voice of the 56% who voted Remain."
The Human Rights Consortium campaign organisation said it was deeply concerned about the risk of entering into a process to withdraw from the EU without ensuring that human rights protections, emanating from EU membership, are first safeguarded.
Director Kevin Hanratty said: "Those safeguards are important elements in the Northern Ireland peace process and need to be protected."
He added: "Northern Ireland now finds itself in a particularly perilous situation with regard to the protection of human rights.
"We face the combined threats of a removal of EU rights protections through Brexit, the threat to the Human Rights Act and withdrawal from the European Convention of Human Rights.
"We face these threats without the full protection that the Belfast/Good Friday Agreement was to afford us, most notably through a local bill of rights.
"Undermining these rights can only be seen as a fundamental threat to the principles of the Belfast/Good Friday Agreement."
Mr Eastwood said his party would vote at Westminster against triggering Brexit talks and challenged Sinn Fein MPs, who do not take their seats, to do the same.
He encouraged all Remain MPs to vote against.