British Prime Minister Theresa May postponed Parliament's vote on her European Union divorce deal on Monday to avoid a potential defeat.
The vote was scheduled to take place on Tuesday. May's office had been insistent that the vote would definitely be held.
The British pound fell sharply against the U.S. dollar after the announcement, hitting an 18-month low.
The move throws Brexit plans into chaos just weeks after Britain and the EU reached an agreement.
Reports have pointed to a big defeat for the prime minister in Tuesday's vote – a result that could sink May's deal, her leadership, or both.
On Monday, the European Court of Justice ruled that the UK can revoke Article 50 and halt Brexit without the permission of other member states.
May's Conservative government does not have a majority in the House of Commons, and opposition parties – as well as dozens of Conservative lawmakers – say they will not back the divorce deal that May and EU leaders agreed upon last month.
Britain voted in 2016 to leave the 28-nation bloc, and invoked Article 50 of the EU's Lisbon Treaty in March 2017, triggering a two-year exit process.
Britain is scheduled to leave the bloc on March 29.
The Associated Press contributed to this story