Britain's Shadow Northern Ireland Secretary says suggestions that the Good Friday Agreement has 'run its course' are incredibly reckless and wrong.
Several pro-Brexit politicians have made comments criticising the agreement in recent days.
It comes as Northern Irish leaders and the British Prime Minister are due to meet today.
The DUP will ask the British Prime Minister to set a budget urgently, but Sinn Féin opposes any form of direct rule by Westminster.
Concerns have been raised about comments from a number of British politicians since the collapse of the latest round of power-sharing talks last week.
Labour MP Kate Hoey told The Huffington Post: “I think there is a need for a cold rational look at the Belfast agreement.
“Even if a settlement had been agreed a few days ago there is nothing to stop Sinn Féin or the DUP finding something else to walk out about in a few months. Mandatory coalition is not sustainable in the long term. "
Former Northern Secretary and Conservative MP Owen Paterson, meanwhile, recently drew criticism for sharing an article suggesting the Good Friday Agreement had 'outlived its use':
— Owen Paterson MP (@OwenPaterson) February 16, 2018
Tánaiste and Foreign Affairs Minister Simon Coveney slammed efforts to 'talk down' the Good Friday Agreement as 'irresponsible and reckless' - later insisting that both the Irish & British governments remain 'absolutely committed' to it.
Talking down Good Friday Agreement because it raises serious and genuine questions of those pursuing #Brexit is not only irresponsible but reckless and potentially undermines the foundations of a fragile peace process in Northern Ireland that should never be taken for granted
— Simon Coveney (@simoncoveney) February 20, 2018
Yesterday, the UK's Northern Secretary Karen Bradley reiterated her government's support for devolution - but also told MPs 'challenging decisions' will have to be made soon, particularly around the need for a budget for Northern Ireland.
Shadow Secretary and Labour MP Owen Smith says the pro-Brexit politicians should not have criticised the Agreement at this delicate time.
He told Newstalk Breakfast: "I think they're incredibly reckless, and I think they're completely wrong.
"They know that sensible people [...] are pointing out that it's very hard to exit the European Union on 'hard' terms without there being a hard border back on the island of Ireland.
"We can all see [that] would be incredibly damaging to prosperity on the island of Ireland, but also I think put at risk the gains we've made in terms of peace in Ireland."
He added: "Even in terms of the idea of a border being put back in Northern Ireland - not even the infrastructure, but the idea of dividing the island again physically - would damage the spirit of the Good Friday Agreement, and would be fundamentally damaging to those people who found reconciliation within the terms of the Good Friday Agreement.
"We've got to sustain the agreement and defend it, because it is the only viable route to peace in Northern Ireland."