UK lawmakers vote to delay key decision on Boris Johnson's Brexit deal

U.K. lawmakers voted to delay a key decision on Boris Johnson's Brexit deal, a blow to the prime minister that will force him to seek another extension from the European Union.

At a rare Saturday sitting, lawmakers supported an amendment introduced by former Conservative lawmaker Oliver Letwin that withholds approval for the deal Johnson struck with the EU this week until legislation is in place. It passed 322 to 306.

By law, Johnson must now send a letter to Brussels asking that Britain's departure be delayed until Jan. 31. However, while speaking after the vote, he indicated he may not abide by the rule, known as the "Benn Act."

The move is intended to prevent the UK from crashing out of the EU without a deal on the scheduled Oct. 31 departure date.

"I will not negotiate a delay with the EU, and neither does the law compel me to do so," he said. "Further delay will be bad for this country."

It's unclear how Johnson could circumvent the law.

A spokesperson for Jean-Claude Juncker, president of the EU Commission, said in a tweet that it's up to the UK government to "inform us about the next steps as soon as possible."

The British government looks set to try again next week to get Parliament to back its divorce deal with the EU. Leader of the House of Commons Jacob Rees-Mogg said the government will seek a debate Monday on its Brexit-implementing legislation that would effectively be a vote to approve the deal.

Lawmakers have twice delayed Britain’s exit from the EU, repeatedly rejecting a similar deal struck between former prime minister Theresa May's government and the trading bloc. The EU eventually agreed to postpone Brexit until Oct. 31; Johnson has previously the UK must leave the EU by the end of October -- even if there’s no deal in place that sets up the parameters of the divorce, like trade and the rights of European citizens living in the UK.

The Associated Press contributed to this report.