The House of Lords, when addressed by the Queen | Pool photo via Leon Nea/Getty Images UK government loses House of Lords vote on Brexit Bill House of Lords reject prime minister May’s ‘take it or leave it’ vote on Brexit deal by 366 to 268.

Members of the House of Lords on Tuesday voted in favor of giving parliament a "meaningful vote" on the outcome of divorce talks with the European Union.

In a blow for U.K. Prime Minister Theresa May, peers voted 366 to 268 in support of an amendment giving parliament the option to send the government back to the negotiating table if it does not support any deal agreed with the remaining 27 EU countries or if no deal is reached. The amendment states that the U.K. parliament must give its approval to the outcome of negotiations with the EU before the European Parliament votes on the agreement.

The British government already suffered a defeat in the House of Lords last week, with peers calling for the rights of EU nationals living in the U.K. to be protected after Article 50 is triggered.

The two amendments backed by the Lords can be reversed when the Bill returns to the House of Commons, expected to take place on 13 and 14 March, which would pave the way for May to notify EU leaders of the U.K.'s intention to quit the bloc in time to meet her self-imposed deadline of triggering Article 50 by April 2017.

David Davis, the Brexit Secretary, issued a statement immediately after the Lords vote to confirm the government would seek to overturn the amendments. The Lords vote was “disappointing” he said. The Article 50 Bill “has a straightforward purpose — to enact the referendum result and allow the government to get on with negotiating a new partnership with the EU,” he said.

“It is clear that some in the Lords would seek to frustrate that process, and it is the government's intention to ensure that does not happen.”

It is expected that, while a handful of MPs may change their minds in light of the Lords’ decision, Theresa May will still have the numbers to knock down both amendments next week. In theory, the Lords could push back again, but it is expected that peers will not put up a fight, recognizing that for the unelected second chamber to block, rather than just amend, the will of the Commons, would risk a constitutional crisis and renewed efforts by the government to reform the House of Lords itself.

However, the scale of the Lords rebellion, and attacks on her strategy by Conservative figures such as Lord Heseltine, is a significant dent to her authority. Critics have ammunition for their claim that she is riding roughshod over parliament with her Brexit strategy.

“The Lords have rightly stood up for parliamentary sovereignty and refused to write the government a blank check for hard Brexit. The Commons must now find the nerve to do the same,” said the Liberal Democrats’ Brexit spokesman Nick Clegg.

Even in the unlikely event that May does lose a Commons vote, she could still trigger Article 50 this month. However, if the amendment on a "meaningful vote" is passed by MPs — an unlikely scenario — it has major implications for her negotiation strategy, opening up the possibility of her final Brexit deal being rejected by MPs in favor of further talks and a surefire recipe for a no confidence vote at home that could lead to an early election.

May had promised a “take it or leave it” vote for parliament. She insisted this position would allow her to walk away from the negotiating table if she does not like any agreement offered by the remaining EU27 countries.

Earlier on Tuesday peers rejected a proposal to hold a second referendum that would allow the U.K. to vote again on whether to leave the EU at the end of divorce talks in 2019.