Canada's broadcasters will not allow Green Leader Elizabeth May to participate in the leaders debates during the federal election campaign, the networks announced Monday afternoon.

The consortium of networks, which includes the CBC, said three of Canada's parties were opposed to May's inclusion, but did not give more details.

In recent days, the Conservatives, Bloc Québécois and the NDP have all expressed their opposition to May joining the debates.

"It became clear that if the Green party were included, there would be no leaders' debate," the consortium said in a press release.

"In the interest of Canadians, the consortium has determined that it is better to broadcast the debates with the four major party leaders, rather than not at all."

May calls decision 'anti-democratic'

The Greens' leader immediately came out firing on the decision, saying her party "may have to take further steps" and will consult with legal advisers about a possible court challenge or injunction against the debate taking place without her.

"I think it really is appalling that the media consortium is willing at this point to rewrite the rules," May said to the CBC's Don Newman on Monday, just minutes after the decision was announced.

She said the Greens are fielding 306 candidates across the country to run "against all those parties that don’t want to see us in the debates."

May also dismissed the consortium's explanation that her presence would cause the other leaders not to show up.

"I don't think Canadians will accept this for a minute," May said. "It's the decision-making of a small group of TV network executives, and to do so without clear rules that are transparent and predictable and applied fairly really is anti-democratic."

The parties that will take part in the debates are the New Democrats, the Liberals, the Bloc Québécois and the Conservatives.

The debates will take place Oct. 1 and 2.

PM: Allowing May into debate 'unfair'

Liberal Leader Stéphane Dion said Monday that his party had supported May's participation, but that he himself would not participate if Conservative Leader Stephen Harper were to boycott the debates.

"I will say that I would like her to be there," Dion said.

Bloc Québécois Leader Gilles Duceppe said that while he never threatened to withdraw over the issue, his preference was to have just the leaders of the four major parties in Parliament, and that the Greens should not be included in the debate because they have not elected an MP to Parliament yet.

In their opposition, the Tories and NDP cited a deal struck by May and Dion, in which they agreed not to run candidates against each other in their respective Nova Scotia and Quebec ridings.

NDP campaign spokesman Brad Lavigne confirmed late Monday that party leader Jack Layton had said he wouldn't attend the debate if May were allowed to participate.

"We believe that as someone who's endorsed Stéphane Dion to be the prime minister of Canada, she has endorsed Liberal candidates throughout the country," Lavigne said.

"We said that if the Liberals were going to have two representatives, we would not accept the invitation."

Harper said letting May participate in the debates would be in essence allowing a "second Liberal candidate" to participate, which he called "fundamentally unfair."

"Elizabeth May is not an opponent of Stéphane Dion," the prime minister said. "She is his candidate in Central Nova, and I think it would be fundamentally unfair to have two candidates who are essentially running on the same platform in the debate," Harper said at a campaign event in Richmond, B.C.

He also said he expected May to endorse the Liberal party before the end of the campaign.

'We are cutting into his base': May

But May dismissed Harper's claims, saying the prime minister was "clearly the leader who has the most to lose here.

"We are cutting into his base," she said. "And frankly, the notion that I would go into debates as someone to cheer on one other party leader is absurd."

The Greens have previously indicated that if they were excluded, they would lodge a complaint with Canada's broadcasting regulator, the Canadian Radio-television and Telecommunications Commission, and might launch a court challenge.

Traditionally, the consortium of Canada's largest English and French television networks — CBC/Radio-Canada, CTV, Global Television and TVA — has decided which party leaders would participate in the debates.

In the December 2005 debates that preceded the 2006 election, Jim Harris — then leader of the Green party — was excluded because his party had no seats in the House of Commons.

Representation in the House of Commons is an "indisputable" criterion for inclusion in the national debate, said the CBC ombudsman in a 2006 report responding to Green party complaints.

Former Independent MP Blair Wilson, who was elected as a Liberal, joined the Greens last month as the party's first member of Parliament.