Democratic Unionist leader Arlene Foster has been lambasted as "not representing" the majority view in Northern Ireland on Brexit.
Sinn Fein deputy leader Michelle O'Neill made her comments after Mrs Foster and Ulster Unionist leader Robin Swann met EU chief negotiator Michel Barnier in Brussels on Tuesday.
Speaking after the meeting, Mrs Foster said she will not back any Brexit deal that could lead to new economic barriers between Northern Ireland and the rest of the UK.
The UK Government has promised to set out further proposals on the "backstop" arrangement aimed at avoiding a hard border with Ireland, with speculation that it could involve regulatory checks on goods travelling between Britain and Northern Ireland.
The EU's proposed backstop would see Northern Ireland effectively remain in the customs union and single market while the rest of the UK shifts away from Brussels' rules, something the Prime Minister has already said would be unacceptable.
Mrs Foster warned her party will not back any Brexit deal unless it matches their red line.
Mr Swann also voiced his party's opposition to the backstop to Mr Barnier.
"We made it clear to him that unionists in Northern Ireland are deeply concerned by the proposed backstop and its implications for our place within the United Kingdom," he said.
"The efforts to de-dramatise do not go to the heart of unionist concerns and we underlined to Michel Barnier why the outworkings of the backstop are so problematic for us."
Ms O'Neill spoke out against the unionist parties, claiming they do "not represent the majority view on Brexit".
"The DUP do not speak for the majority of people here on Brexit, just as they do not on a range of social issues, including the rights of women, Irish speakers, victims and the LGBT community," she said.
"I also believe that Arlene Foster's so-called blood red lines are out of step with many in the unionist community who are growing increasingly concerned at the DUP's willingness to endanger our economy in order to avoid an imaginary line on the Irish Sea."
Ms O'Neill, along with the leaders of the SDLP, Alliance Party and Green Party, met with Mr Barnier last week.
"We did so as the majority voice of the people here," she said.
"All those parties made it clear that, in terms of Brexit, the DUP should not have a veto.
"We also re-iterated our common position that the 'backstop' as already agreed must be maintained and is the absolute bottom line for Sinn Fein, SDLP, Alliance and Green Party as we enter the endgame of the Brexit negotiations."
SDLP MLA Claire Hanna also criticised the DUP's position on Brexit.
"The DUP wanted Brexit, campaigned for Brexit and funded Brexit, but they do not acknowledge the reality of Brexit.
"The DUP need to review their contradictory red lines and accept either full alignment with the single market and customs union, or some regulatory checks."
Alliance MLA Stephen Farry added: "The DUP is not representing this region's economic and political interests. Their current stance is taking us over the cliff to a no-deal Brexit."