A move to ensure the government takes on board the Good Friday Agreement during Brexit negotiations has been rejected by MPs.
The Social Democratic and Labour Party (SDLP) proposed the amendment to the Brexit bill which paves the way for the UK's withdrawal from the EU.
It was defeated by 327 votes to 288.
MPs approved the bill, backed by the Democratic Unionist Party and Ulster Unionist Party, without amendment on Wednesday.
SDLP MPs and Independent MP Lady Hermon voted against it.
On social media, SDLP leader Colum Eastwood said he was "very proud" of his three MPs for their "fight to protect us and the Good Friday Agreement".
Commenting on the vote, Sinn Féin President Gerry Adams said: "This decision confirms my worst fears. The British government doesn't care one iota for the people of the north."
DUP MP Sammy Wilson said: "DUP MPs supported the government throughout the bill's passage to ensure there were no changes introduced that would frustrate or delay Brexit, dilute Northern Ireland's position within the United Kingdom or deny the electorate their wishes.
"Amendments such as those tabled by the SDLP and SNP were simply another attempt to frustrate the will of the people and I am delighted they were not successful."
Lady Hermon said she still had not been persuaded that Brexit would be good for the country.
"I hope to be proved wrong, and look forward with particular curiosity to see how a seamless, frictionless border is achieved with the Republic of Ireland," she added.
David Ford, from the Alliance Party, said unionists had "put our current political system at risk" by not backing the amendment.
"The vote against this amendment is deeply worrying as it leaves our institutions without protection as the exit process gets underway," he added.
Ulster Unionist Party MP Tom Elliott commented: "The Irish ambassador to the UK, Daniel Mulhall, confirmed there is an absolute determination from the Irish government to ensure the 1998 agreement is not impacted by Brexit.
"We supported the EU (Notification of Withdrawal) Bill, which was designed to obtain Parliamentary approval to trigger Article 50. Our approach to amendments was to keep our focus on the intended purpose of the bill."
The bill will now move to the House of Lords.
Prime Minister Theresa May wants to trigger formal Brexit talks by the end of March.