The British Prime Minister is to give a speech on Brexit in Northern Ireland tomorrow, her spokesman has said.
Theresa May is due to address British commitments regarding the border and meet local business owners during her visit.
She will also meet DUP leader Arlene Foster in Belfast.
Mrs Foster said she would tell Mrs May that the proposed backstop "drives a coach and horses through the Belfast Agreement's principle of consent".
She said it would effectively create a new border between Northern Ireland and the rest of the UK.
"Parliament has spoken," Mrs Foster said.
"A majority has rejected the current backstop. The European Union must now accept the need for the withdrawal agreement to be reopened. The toxic backstop must be dealt with."
Mrs Foster said that the DUP wants "an orderly exit from the European Union which works for London, Dublin, Belfast and Brussels".
"It is possible but requires political will," she said.
"This is not a time for intransigence. It is time to respect unionists and nationalists alike in Northern Ireland and deliver a deal which is sensible and practical."
The EU's chief Brexit negotiator Michel Barnier reiterated today that the Withdrawal Agreement cannot be reopened, saying "the backstop was only operational solution to address Irish border issue".
Dialogue @EU27 continues #Brexit. Today in The Hague with @MinPres Mark Rutte: full agreement that Withdrawal Agreement cannot be reopened. Backstop = only operational solution to address Irish border issue today. EU ready to work on alternative solutions during transition. pic.twitter.com/YsCNI10K71
— Michel Barnier (@MichelBarnier) February 4, 2019
Elsewhere, Dutch Foreign Minister Stef Blok has visited the border between Louth and Armagh, accompanied by Minister of State for European Affairs Helen McEntee.
Mr Blok said it was very important for him to see with his own eyes "the border that isn’t a border".
He pointed out that "there is a line in the tarmac", which he said was not unlike the line between municipalities in the Netherlands.
Mr Blok tells the media he wanted to see the border here and is very committed to avoiding a hard border @rtenews pic.twitter.com/E7MidCjnUr
— Sinéad Hussey (@SineadHus) February 4, 2019
Mr Blok has dismissed the idea of reopening the Brexit deal, saying it was unreasonable after such long negotiations to now expect a different agreement.
Mr Blok said the EU staying united was the only way of securing a deal.
Ms McEntee said there had already been compromise and peace on the island needed to be protected.
She said this was not about scaremongering about the risks to the border in the event of a hard border, but was about protecting a peace that had taken 20 years to develop and was still very fragile.
The announcement of Mrs May's visit to Belfast came as British Labour's spokesperson on Brexit Keir Starmer said that in the current circumstances, a backstop was inevitable.
Mr Starmer had arranged to be in Belfast today for meetings with the SDLP and Sinn Féin, as well as with business leaders and the Irish Congress of Trade Unions.
He said that following Mrs May's U-turn on her own Withdrawal Agreement last week, a backstop arrangement, not time-limited, was inevitable.
He also said the longer-term solution as the UK leaves the EU is a comprehensive customs union and single market alignment. Both the SDLP and Sinn Féin welcomed his comments.
In recent weeks, Mrs May's views have aligned with the stance of the DUP, whose ten MPs keep her in power at Westminster.
Meanwhile, former Northern Ireland first minister David Trimble has announced he is planning to take the British government to court over his claim that the Northern Ireland protocol in Mrs May's Withdrawal Agreement breaches the terms of the Good Friday Agreement.
Mr Trimble, who shared the Nobel Peace Prize with John Hume in 1998, said he would initiate judicial review proceedings to ensure that the protocol, which includes the backstop, is removed from the Withdrawal Agreement.
He said that alternative arrangements should be put in place instead, along the lines suggested in the documents produced by Eurosceptic opponents of Mrs May's agreement.
Last week, proposed changes to the Withdrawal Agreement were drawn up by British Housing Minister Kit Malthouse in the House of Commons.
It proposes to recast the backstop as what they term, a "free trade agreement-lite", with a commitment on all sides there should be no hard border on the island of Ireland.
It requires Mrs May to replace the Withdrawal Agreement's backstop with "alternative arrangements" to keep the Irish border open after Brexit.
Mrs May told the Commons last week it was "a serious proposal that we are engaging with sincerely and positively".
