Arlene Foster has accused the Prime Minister of trying to force people into backing her Brexit deal.
The Democratic Unionist leader described Theresa May’s approach to Brexit as “weak” and damaging to the UK.
She made the comments ahead of her meeting with the EU’s chief Brexit negotiator Michel Barnier.
She will be joined by Northern Ireland MEP Diane Dodds as well as Conservative MPs Iain Duncan Smith and Owen Paterson at Thursday’s meeting.
“This is a useful opportunity to once again set out why we oppose the Withdrawal Agreement and urge the EU’s chief negotiator to acknowledge the concerns of those we represent in Northern Ireland by making the changes outlined by Parliament on 29 January.
“We want to see a sensible deal which works for every part of the United Kingdom and respects the referendum result.
“However, we cannot settle for a deal which would undermine the economic and constitutional integrity of the United Kingdom.”
The DUP’s 10 MPs had been supporting the minority Government in key decisions but have voted against Mrs May’s proposed deal.
They adamantly oppose the backstop insurance policy which they believe would redraw the border with the EU down the Irish Sea and threaten the integrity of the UK and Northern Ireland’s place in it.
Mrs Foster added: “The European Union has spoken much about protecting the peace process and the Belfast Agreement but has consistently ignored the views of unionists who do not want a new border erected between Northern Ireland the rest of the UK.
“Despite the Prime Minister being warned about the opposition to her Withdrawal Agreement, she has limped along and tried to force people into a cul-de-sac where they have no option but to support her deal.
“That is a weak approach and demeans the strength of this great nation.
“It is also foolish as it traps the UK and burdens future generations with a bad deal.
“Our great democratic principles have been damaged.”
She said it was “outrageous” that almost three years after people voted to leave the European Union, the UK could potentially face another European election.
“The uncertainty we face is not the fault of the voters,” she continued.
“The Prime Minister should recognise that the decision to leave the EU is not the problem but rather the ham-fisted manner in which the negotiations have taken place.”