British lawmakers on Tuesday rejected Prime Minister Theresa May’s Brexit deal, voting against it by 432 to 202, BBC reported. It is believed to be the biggest defeat ever suffered by a British prime minister in Parliament since 1918.

The legislators who voted against the agreement, struck between the European Union and the United Kingdom government, included MPs of May’s own Conservative Party. The agreement sets out terms of Britain’s exit from the European Union on March 29.

“It is clear that the House does not support this deal, but tonight’s vote tells us nothing about what it does support,” May told Parliament. “Nothing about how – or even if – it intends to honour the decision the British people took in a referendum parliament decided to hold.”

Opposition Labour Party leader Jeremy Corbyn called for a vote of no confidence, which will be held on Wednesday. If the government is voted out, it will have 14 days to overturn the result or face a national election. However, May is likely to survive the vote, unless MPs from her own party vote her out of power.

British and European Union leaders in November 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.

The prime minister has said she will hold talks with the Opposition and Northern Ireland’s Democratic Unionist Party to see what would be required to ensure the support of the House. However, if no withdrawal agreement is finalised before March 29, the United Kingdom will leave the European Union without a deal. This will mean European Union laws and customs and the free movement of people, goods and services will cease overnight.