Sinn Fein has accused the DUP of showing a reckless disregard for the Good Friday Agreement after leader Arlene Foster claimed the peace deal was not sacrosanct.
Sinn Fein president Mary Lou McDonald insisted the 1998 accord between the UK and Irish Governments must not become a bargaining chip in the Brexit negotiations.
She reacted angrily after Mrs Foster suggested the terms of the agreement could be altered in efforts to strike an EU exit deal.
"Today's comments by DUP leader Arlene Foster on the Good Friday Agreement are unacceptable and reveal a reckless disregard for the peace process, prosperity and progress," said Mrs McDonald.
Critics of Brexit on the island of Ireland have warned of its potential to undermine aspects of the international treaty, including its provisions for cross-border co-operation and rights protections.
The DUP campaigned against the Good Friday Agreement when it was resoundingly endorsed in referenda on both sides of the border in 1998.
Elements of the deal have been altered by subsequent political agreements in Northern Ireland, such as the 2006 St Andrews Agreement.
In an interview with the Daily Telegraph, Mrs Foster said: "It has been deeply frustrating to hear people who voted Remain and in Europe talk about Northern Ireland as though we can't touch the Belfast Agreement. Things evolve, even in the EU context.
"There has been a lot of misinterpretation, holding it up as a sacrosanct piece of legislation."
In response, Mrs McDonald called on the Irish Government to make clear that the terms of the deal would be protected.
"It should be remembered that Arlene Foster left the UUP, which supported the Good Friday Agreement, to join the anti-agreement DUP," she added.
"It appears the DUP leader has learnt nothing over the past 15 years."
Brexit is incompatible with the Good Friday Agreement. The actions of the DUP and their deal with the Tories is bad for our economy and undermines the rights of citizen
The latest row between the DUP and Sinn Fein comes amid the ongoing political impasse in Northern Ireland following the collapse of the powersharing institutions in early 2017.
"The Good Friday Agreement was endorsed by the vast majority of people north and south," said the Sinn Fein president.
"It is the people's agreement and not a chip to be bargained with as part of any Tory/DUP Brexit deal.
"Brexit is incompatible with the Good Friday Agreement. The actions of the DUP and their deal with the Tories is bad for our economy and undermines the rights of citizens.
"The DUP should commit to the full implementation of the Good Friday, and other agreements, rather than seeking to undermine them.
"This would unlock the pathway to re-establishing the political institutions and safeguarding the interests of all the people in the north."