The resignations come just two days after May secured the backing of her cabinet for a plan to keep close ties to the European Union after leaving the bloc. Davis and Baker, both longstanding euroskeptics, decided they could not support the policy, a person familiar with the matter said.

May’s office confirmed that Davis had resigned but had no comment yet on the reasons.

Davis, Baker and other pro-Brexit members of May’s Conservative party held deep concerns about her plans for keeping the U.K. tied to EU rules for goods and adopting a close customs arrangement with the other 27 member countries.

They feel Britain should have a clean break from the bloc and be liberated to pursue new trade deals with other countries, as well as to make its own laws, free from European influence.

As the minister responsible for the Brexit negotiations, Davis is a major voice in the debate in the U.K. The double resignation on Sunday has the potential to derail May’s government and set in motion a chain of events that could lead to an attempt to oust her as prime minister. Their stand may embolden pro-Brexit lawmakers to make a move against her.

It comes at a critical and highly sensitive time for May’s strategy, as she seeks to make progress in negotiations in Brussels. A divorce agreement is due to be wrapped up in just 15 weeks, but there are still major obstacles to overcome.

On Friday May achieved a rare consensus in a key cabinet meeting at her Chequers country house estate on the way forward for the negotiations with the EU. That was meant to kick-start talks that have been stalled for months.

Second Thoughts

Davis and fellow Brexit backer Foreign Secretary Boris Johnson both agreed to support May’s proposal for a softer divorce than she had originally planned, and it seemed she had survived the storm. Johnson’s allies said on Saturday he decided not to quit as he wanted to remain in government to fight for the kind of Brexit he campaigned for.

Yet after reflecting on the situation, Davis and Baker apparently decided they could not live with such a soft Brexit after all.

May will have a key meeting with members of her Tory party to discuss her plan in Parliament on Monday. Some lawmakers have already expressed their misgivings.