The Liberal government is defending its decision to exclude two indigenous groups from a meeting with Prime Minister Justin Trudeau to discuss the development of a climate change policy.

A government spokesperson told CTV News the three groups meeting with Trudeau represent Aboriginal Peoples whose rights are enshrined in the Constitution.

The prime minister invited Clement Chartier of the Metis National Council, Perry Bellegarde of the Assembly of First Nations and Natan Obed of Inuit Tapiriit Kanatami to meet with him and the premiers in advance of the First Ministers' Meeting on climate change.

But the Congress of Aboriginal Peoples, which represents those living off-reserves, and the Native Women's Association of Canada, were not invited to Thursday's meeting.

Congress of Aboriginal Peoples National Chief Dwight Dorey said he was confused about why he was invited to attend the United Nations Climate Change Conference in Paris late last year, but not to this meeting with Trudeau.

"Previously, I had met with the prime minister and other leaders and he said all five national indigenous organizations would be involved on important issues that affect us. Climate change affects everybody," he said. 

Noting Section 35 of the Constitution Act, which recognizes and affirms the rights of aboriginal Canadians including, “the Indian, Inuit and Métis peoples of Canada," Dorey said, "The word 'includes' is very significant and important.

“That was put in there to make sure nobody was excluded. But we're seeing today that a large portion of the population in this country in Canada, of rights-based people, are being excluded," he said. "That's discriminatory." 

Dorey said it affects his confidence, too, that the prime minister is keeping his promise to work with Canada's indigenous peoples.

The estimated 1.1 million aboriginal peoples living off reserves need a voice, he says.

"The Congress of Aboriginal Peoples is their voice. We need to be involved if the prime minister is going to talk seriously about partnership building. Let's build it and not exclude anybody."

Trudeau has said there will be other chances for the groups excluded from Thursday's meeting to make their opinions known, at future conferences.

"I have had, over the past months, many meetings both with the national aboriginal organizations together but also individually with leaders and communities and the activists from the indigenous community to talk about the issues facing them," Trudeau told reporters in Vancouver on Wednesday.

With files from The Canadian Press