The campaign for Patrick Brown said it was consulting its legal team after the leadership election organizing committee of the federal Conservatives voted to disqualify him from the race late Tuesday.
Ian Brodie, the chair of the committee, announced the stunning move in a written statement after a meeting to discuss the matter.
He said the party had recently become aware of "serious allegations of wrongdoing" by the Brown campaign.
The allegations are related to the financing rules in the Canada Elections Act, Brodie said, but provided no further details.
The Brown campaign responded with a statement accusing the party of basing its decision off "anonymous allegations" and without providing the full details or evidence.
It accused the party of going on a "fishing expedition" and not giving the campaign "ample time" to respond, but said it "still complied with every bizarre request and unsubstantiated claim."
It went on to say the move disenfranchises thousands of Brown supporters, who purchased a party membership by the June 3 deadline to pick his name on the Conservative party's ranked ballot.
"This is reprehensible, undemocratic behaviour that breaks faith with hundreds of thousands of Canadians that embraced Patrick Brown's vision of a modern, inclusive Conservative party," said the statement.
In his statement late Tuesday night, Brodie said the chief returning officer for the party informed Brown of the concerns it received regarding the financing of his campaign, requesting a written response, and decided to withhold the interim membership list from his campaign.
Brodie said the response from Brown's campaign did not satisfy the concerns and the chief returning officer recommended the leadership election organizing committee disqualify him, which voted to do so.
Brodie said the party will be sharing what it has with Elections Canada.
He said both he and the party's chief returning officer did their best to be fair to Brown, who is the current mayor of Brampton, Ont., and a former leader of the Ontario Progressive Conservatives. He also said they did their best to provide time to refute the allegations.
"None of these problems has any impact on the integrity of the vote itself," Brodie said.
"While we felt it important to provide a transparent response to party members about this matter, because this issue is now subject to further investigation, we will not be speaking further on the subject."
The Brown campaign accused the party of acting in favour of the leadership candidate considered to be his main rival for the top job.
"Why is the party doing this? It was expecting a coronation for Pierre Poilievre," said the statement.
The campaigns for Poilievre, a longtime Ottawa-area MP, and Brown have been attacking one another throughout the race.
Poilievre had not yet responded to the leadership election organizing committee's decision by late Tuesday night.
The campaign for former Quebec premier Jean Charest, who is also in the leadership contest, did respond by calling the news "deeply troubling."
"We expect further communications on the allegations of wrongdoing," wrote Charest campaign spokeswoman Michelle Coates-Mather.
"Transparency is paramount. We need to understand what the allegations are and how Patrick Brown's campaign responded."
The Conservatives will announce the winner of the leadership race in Ottawa on Sept. 10.
The other candidates in the race are Leslyn Lewis and Scott Aitchison, Conservative MPs from Ontario, as well as Roman Baber, a former Independent member of the Ontario legislature.
Although he has been disqualified, his name is expected to still appear on the ranked ballot. A party spokesman said late Tuesday that a large batch of them had already been sent to members in the mail.
Last week, the party said about 675,000 members have signed up to vote for a new leader of the Conservatives.
This report by The Canadian Press was first published July 5, 2022.
Stephanie Taylor, The Canadian Press