A concerted effort to unseat Speaker John A. Boehner was under way the day of his re-election to the position, but participants called it off 30 minutes before the House floor vote, CQ Roll Call has learned.

A group of disaffected conservatives had agreed to vote against the Ohio lawmaker if they could get at least 25 members to join the effort. But one member, whose identity could not be verified, rescinded his or her participation the morning of the vote, leaving the group one person short of its self-imposed 25-member threshold. Only 17 votes against Boehner were required to force a second ballot, but the group wanted to have insurance.

Even with 24 members, the group would easily have been able to force a second ballot round, but the effort was aborted in frenetic discussions on the House floor.

“There was an effort to get to a particular number,” said one Republican member who voted for Boehner but was familiar with the effort to oust him.

Republican Reps. Justin Amash of Michigan, Mick Mulvaney of South Carolina and Raúl R. Labrador of Idaho played key roles in organizing the plot. But participants describe its origin as organic and not led by any particular member, despite the suggestion by at least one House Republican that Amash was the ringleader.