The House of Lords has backed a Brexit bill amendment requiring parliament to approve any exit deal that Britain makes with the EU, putting the government under further pressure to meet an end-of-March deadline to trigger Article 50.

The vote was passed Tuesday evening by 366 votes to 268. Peers voted on an amendment to the Brexit bill over whether MPs should get a “meaningful vote” on the final outcome of negotiations with the EU.

The amendment tabled in the House of Lords by Labour, and backed by leading crossbench peers, demands that Parliament must approve the result before May can conclude any deal on leaving the EU or establishing a new relationship with the bloc.

In a statement following the vote David Davis, Secretary of State for Exiting the European Union, described the passing of the vote as “disappointing.”

“It is clear that some in the Lords would seek to frustrate that [Brexit] process, and it is the Government’s intention to ensure that does not happen,” Davis added. “We will now aim to overturn these amendments in Commons.”

Prime Minister Theresa May had urged peers to reject the amendment, saying it would tie her hands and encourage the EU to refuse to offer the UK a fair agreement.

The PM has promised Parliament a vote, but only on a ‘take it or leave it’ basis, which would see the UK crash out of the EU without a deal if MPs reject the agreement she obtains – an outcome referred to as a ‘hard Brexit.’

May believes she must be able to convince EU negotiators and other member states she is ready to walk away from the table if she does not like what is on offer.

The latest blow to the government comes after peers voted last week in favor of guaranteeing the rights of EU residents to remain in the UK before triggering Article 50.

The passing of amendments means the ‘EU (Notification of Withdrawal) Bill’ will have to go back to the Commons for more votes, a process known as ‘ping-pong.’

The government said it will overturn any amendments when the bill is passed back to the House of Commons. It has suggested it will sort out an agreement on EU citizens living in the UK and British citizens living on the continent as soon as talks get underway.

The bill is expected finally to be passed by both houses at the start of next week, clearing the way for May to notify other European leaders of Britain’s intention to quit the bloc.

Another amendment, calling for a second national referendum at the end of negotiations with the EU, was rejected by peers on Tuesday.