The United Kingdom’s House of Lords voted on Monday to give the Parliament power to block or delay the Theresa May government’s final deal on Britain’s departure from the European Union.

The House of Lords, which is the upper chamber of the British Parliament, voted 335 to 244 in favour of an amendment that could force Britain to renegotiate the deal with the European Union in Brussels or even halt the Brexit process, Reuters reported. The government could overturn the amendment in the House of Commons, where it has a thin majority, the network said.

“We are disappointed that the House of Lords has voted for this amendment in spite of the assurances we have provided,” Britain’s Minister for Exiting the European Union Lord Martin Callanan said, according to PTI. “What this amendment would do is weaken the United Kingdom’s hand in our negotiations with the European Union by giving Parliament unprecedented powers to instruct the government to do anything with regard to the talks, including keeping the country in the European Union indefinitely.”

In March, Britain and the European Union agreed on the terms for Brexit. The Theresa May government reached an agreement on Brexit after making a series of concessions to Brussels, and accepting a plan to keep Northern Ireland under European law. The two sides also reached an agreement on the rights of 4.5 million European Union citizens who live in the UK and the 1.2 million British citizens who live in member nations of the European Union.

The European Union has said that Britain must leave the bloc by December 31, 2020.