Graham Brady, chairman of the party’s so-called “1922 committee”, said the threshold for a vote had been exceeded.
The decision on May’s future as prime minister will be made later on Wednesday in the House of Commons as Britain’s planned divorce from the European Union was plunged into chaos.
A ballot will be held between 18:00-20:00 GMT on Wednesday in the House of Commons and an announcement made as soon as possible afterwards, Brady said.
More to follow.
Al Jazeera and news agencies