British Prime Minister Theresa May on Monday said she has called off an MPs vote scheduled for Tuesday on the Brexit deal with the European Union, because it “would be rejected by a significant margin”. May claimed that while MPs back much of the deal she has signed with the European Union, there is disagreement over the Northern Ireland backstop proposals, BBC reported.

British and European Union leaders last month committed to avoiding a “hard border” between Northern Ireland and the Republic of Ireland after Brexit. The backstop is a “safety net” which will preserve a border without customs and regulatory checks through a series of measures. There are differences between the United Kingdom and the European Union over the terms of this backstop.

On Monday, May told the House of Commons she believed the deal would be successful if she managed to ally the concerns of legislators. The prime minister said she would defer the vote until after she spoke to European Union leaders ahead of a summit this week, on the backstop matter.

However, Speaker John Bercow said the government should allow a vote on whether the vote scheduled for Tuesday should be cancelled. Bercow said some legislators were angry about the cancellation.

The European Court of Justice, responding to a plea by Scottish legislators, ruled on Monday that the UK can unilaterally revoke its decision to leave the European Union without the permission of the other member states. However, May ruled out this option, and defended the Brexit deal.

“It is the right deal for Britain,” she asserted. “I am determined to do all I can to secure the reassurances this House requires, to get this deal over the line and deliver for the British people.”

But Labour Party leader Jeremy Corbyn claimed May had “lost control of events”, and that the Conservative Party government is in “complete chaos”. He called on the prime minister to resign.