Theresa May has told MPs she will seek to re-open negotiations with the EU over the Northern Ireland backstop, the BBC reports.
The PM said she would go back to Brussels to get a "significant and legally binding change" to the controversial proposal, which aims to stop the return of border checks.
The EU has said it will not change the legal text agreed with the UK PM.
Mrs May said she knew there was a "limited appetite" in the EU, but she believed she could "secure" it.
She is expected to have phone calls with key EU leaders throughout the day ahead of a series of Commons votes over the future direction of Brexit, and has already spoken to the President of the European Commission Jean-Claude Juncker and the Irish Taoiseach (Prime Minister) Leo Varadkar.
Mrs May said the vote later would be a chance to "send a clear message" to EU on the backstop.