Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

LONDON — Three pro-E.U. lawmakers from Britain's ruling Conservatives quit over the government's "disastrous handling of Brexit" on Wednesday, in a blow to Prime Minister Theresa May's attempts to unite her party around plans to leave the European Union.

The lawmakers, long critical of May's Brexit strategy which they believe is being driven by figures on the right of the party, said in a statement they would join a new group in parliament set up earlier this week by seven former opposition Labour politicians.

The resignations put May in an even weaker position in parliament, where her Brexit deal was crushed by lawmakers last month when euroskeptics and E.U. supporters voted against an agreement that both sides say offers the worst of all worlds.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

They could also undermine May's negotiating position in Brussels, where she is going later on Wednesday for talks with Commission President Jean-Claude Juncker to try to secure an opening for further technical work on revising the agreement.

With only 37 days until Britain leaves the E.U., its biggest foreign and trade policy shift in more than 40 years, divisions over Brexit are redrawing the political landscape. The resignations threaten a decades-old two-party system.

"The final straw for us has been this government's disastrous handling of Brexit," the three lawmakers, Heidi Allen, Anna Soubry and Sarah Wollaston, said in a statement.

Soubry later told a news conference that the Conservative Party had been taken over by right-wing, pro-Brexit lawmakers.

"The truth is, the battle is over and the other side has won. The right-wing, the hard-line anti-E.U. awkward squad that have destroyed every (Conservative) leader for the last 40 years are now running the ... party from top to toe," she said.

May said she was saddened by the decision and that Britain's membership of the E.U. "has been a source of disagreement both in our party and in our country for a long time."

"But by ... implementing the decision of the British people we are doing the right thing for our country," she said, referring to the 2016 referendum in which Britons voted by a margin of 52-48 percent in favor of leaving the bloc.

The three sat in parliament on Wednesday with a new grouping which broke away from the Labour Party earlier this week over increasing frustration with their leader Jeremy Corbyn's Brexit strategy and handling of accusations of anti-Semitism.

Another former Labour lawmaker joined their ranks late on Tuesday, and several politicians from both the main opposition party and Conservatives said they expected more to follow from both sides of parliament.

For May's Brexit plan, the resignations are yet another blow to more than two years of talks to leave the E.U., which have been punctuated by defeats in parliament, heated arguments over policy, and a confidence vote which she ultimately won.