Conservative MPs are set to hold a vote of no confidence in UK Prime Minister Theresa May's leadership.

The challenge to her leadership will push Britain into a new era of chaos as it attempts to secure a Brexit deal to leave the European Union.

May said she would fight the challenge.

More than 15% of Conservative MPs submitted a letter calling on her to quit.

Conservative MPs are set to hold a vote of no confidence in UK Prime Minister Theresa May's leadership on Wednesday evening after more than 48 Conservative MPs submitted letters calling for her to stand down.

The challenge to her leadership threatens to plunge the UK government into a protracted period of uncertainty, making May's attempt to get a Brexit deal with the European Union much harder.

The stakes could not be higher. May has so far failed to persuade the UK Parliament to approve the deal she negotiated with the EU, which UK politicians fear could keep Britain wedded to EU rules for years after the separation without the full advantages of EU membership. Earlier this week she canceled a planned vote on the deal to prevent a defeat that threatened to be the largest for a siting prime minister in decades.

Even if May survives the latest challenge, her prospects of winning support for her deal in Parliament look slim.

It could raise the possibility of Britain either dropping out of the EU with no deal — widely regarded as the worst-case scenario, economically — or pursuing a closer arrangement, such as the one enjoyed by Norway. Other possibilities in the mix include a second referendum, which would give the British a chance to back out of Brexit, and a new general election, which could see the Conservatives lose to Jeremy Corbyn's Labour Party.

A statement by the chairman of the 1922 Committee of Conservative MPs, Graham Brady, on Wednesday morning confirmed that 15% of Conservative MPs had called for May to quit, meaning a vote on her future would go ahead.

'I will contest that vote with everything I have got'

The prime minister said she would fight the challenge against her.

"There will now be a vote of confidence in my leadership," May said in a statement outside 10 Downing Street.

"I will contest that vote with everything I have got."

Live coverage: Theresa May battles for survival ahead of Conservative Party no-confidence vote

She said a successful challenge against her would inevitably lead to her successor being forced to delay or even stop Brexit.

A threat to Brexit

"One of their first acts would have to be extending or rescinding Article 50, delaying or even stopping Brexit when people want us to get on with it," she said.

"A change in leadership will put our country's future at risk and create uncertainty when we can least afford it.

"The only people whose interests would be served would be Jeremy Corbyn and John McDonnell," the Labour leader and the shadow chancellor.

A ballot by Conservative MPs will take place Wednesday evening, with the prime minister addressing her backbenchers starting at 5 GMT, or noon ET.

The 1922 Committee chair, Brady, said the ballot would take place between 6 p.m. and 8 p.m. GMT on Wednesday. The result is expected around 9 p.m.

May must win half the votes to put down the rebellion

Under party rules, more than half of Conservative MPs must support the challenge for a full contest to go ahead.

If May were to be successful in such a vote, then another ballot on the question of her leadership could not be held for another year.

If she loses the vote, she will be excluded from any contest. Conservative MPs will then select two candidates to vote on for the job of leader, which will then be voted on by all party members.

Brady told Sky News that the parliamentary stage of the process could be completed before Christmas but that any vote by the party membership would take significantly longer.

Any successful challenge would inevitably lead to calls for a Brexit delay through an extension or withdrawal of the Article 50 process.

'In the national interest, she must go'

In a statement, the chairman and the deputy chairman of the European Research Group of Conservative MPs, Jacob Rees-Mogg and Steve Baker, called on May to quit right away.

"Theresa May's plan would bring down the government if carried forward," they said. "But our party will rightly not tolerate it. Conservatives must now answer whether they wish to draw ever closer to an election under Mrs. May's leadership. In the national interest, she must go."

May, however, received support from the home secretary, Sajid Javid, who is seen as one of the favorites to succeed her.

"The last thing our country needs right now is a Conservative Party leadership election," he tweeted on Wednesday.

"Will be seen as self-indulgent and wrong. PM has my full support and is best person to ensure we leave EU on 29 March."

She was also backed by the work and pensions secretary, Amber Rudd, who tweeted: "The PM has my full support. At this critical time we need to support and work with the PM to deliver on leaving the EU, & our domestic agenda - ambitious for improvements to people’s lives & to build on growth of wages & jobs."

Other rumored leadership contenders, including Penny Mordaunt and Jeremy Hunt, also tweeted their support for the prime minister.

'Theresa May's weakness and failure has completely immobilized the government'

The opposition Labour Party accused the Conservative Party of putting the country's future at risk.

"With only weeks left before Britain leaves the EU, Theresa May's weakness and failure has completely immobilized the government at this critical time for the country," the Labour Party chair, Ian Lavery, said.

"The prime minister's half-baked Brexit deal does not have the backing of her Cabinet, her party, Parliament, or the country.

"The Conservative Party's internal divisions are putting people's jobs and living standards at risk."

Read Graham Brady's letter