The draft Brexit agreement outlined and published by the European Union on Wednesday, which foresees a "common regulatory area" between Northern Ireland and the EU, is unacceptable, UK Prime Minister Theresa May said Wednesday.
"No UK prime minister could ever agree to it," May told lawmakers in the House of Commons less than one hour after the draft was published.
"The draft legal text the Commission have published would, if implemented, undermine the UK common market and threaten the constitutional integrity of the UK by creating a customs and regulatory border down the Irish Sea," May was quoted by the Press Association as saying.
"I will be making it crystal clear to [European President Jean-Claude Juncker] and others that we will never do so," she said.
The EU's draft withdrawal agreement includes a proposal to effectively keep Northern Ireland inside the bloc's single market and customs union in order to ensure there will be no hard border with Ireland, an EU member state.
It says the plan would only come into effect if no other solution to the border issue can be found.
The draft was adopted by EU commissioners on Wednesday before going to the remaining 27 EU states and then to Britain.
The clock is ticking for both sides to finalize the withdrawal agreement and then ratify it before March 29, 2019, the date Britain leaves.
The EU and Britain are separately negotiating a framework for future relations.
May will give a keynote speech on Friday finally setting out her vision for those post-Brexit ties, while the EU will set out its own red lines at a summit in March.
Pressure on May mounted this week when opposition Labour leader Jeremy Corbyn announced a policy shift in favor of staying in a customs union with the EU.
Barnier said Tuesday he agreed with EU President Donald Tusk's view that so far, most of London's demands for trade after Brexit are "pure illusion."
Tusk meets May in London on Thursday as part of what he has called a "critical week" for Brexit talks.