The 2015 federal leaders' debate could see Green Party Leader Elizabeth May and Bloc Québécois Leader Mario Beaulieu square off against Prime Minister Stephen Harper, NDP Leader Tom Mulcair and Liberal Leader Justin Trudeau.

CBC News has learned the consortium of television broadcasters that arranges the federal election debates has issued letters to Canada's major federal parties, inviting them to a meeting next week in Toronto, and has included May and Beaulieu. The consortium will negotiate with the parties to set the terms of the debates, including the format and dates.

It would be the second time May is included in the federal leaders' debates. The Green Party leader took part in the 2008 election debates before she was cut out of them four years ago.

In 2011, May took the consortium to Federal Court to argue she should be included in the leaders' debates. At the time, she did not have a seat in the House of Commons.

In 2008, one MP had crossed the floor from the Liberals to become an independent and then went to the Green Party. The House wasn't sitting at the time, so the party had no MP actually in the House.

The party did, however, receive one million votes in 2008. The May 2, 2011, election ushered in the Green Party leader as its first sitting Canadian MP. The Greens attracted a second MP, Bruce Hyer, after he left the NDP.

While May could be included in both French- and English-language debates, Beaulieu is being considered for French alone.

Mulcair seeks multiple debates

While the BQ was the third party in the House before the 2011 election, with 47 MPs, it was reduced to four following the election and then further splintered. The BQ currently has two seats, the same number as the Green Party.

Parties need at least 11 seats to be considered official parties in the House.

May said she interprets the letter as a commitment that she'll be at the debates.

"I'm relieved, but I also find this the only acceptable conclusion," she said in an interview with CBC News.

"It's actually a question of whether you're considered to be a real party or not."

There was one English-language and one French-language debate in 2011, although Mulcair has suggested he'd like to see more.

"I'm a big fan of debates, as you might have noticed. I enjoy the back-and-forth of a lively debate, and the more open, the better," he said on Feb. 25.

"And frankly, if there was [a] leaders' debate every week of the next election campaign, I'd be there front and centre. I'd really enjoy that."

Mulcair said he'd like to see a full debate devoted to women's issues and one for environmental issues.

A spokeswoman for Trudeau said the Green Party should "have a seat at the table," both in the consortium negotiations and at the debates.

"The environment is a critical issue facing Canadians and ‎Elizabeth May will be an important part of bringing that to the leaders' debates," Kate Purchase said in an email.