The Council of Yukon First Nations and the two Kaska First Nations are condemning the government's move to amend the Yukon Oil and Gas Act.
They issued a joint statement saying a 1997 agreement was signed 'in good faith' by all Yukon First Nations.
That agreement allowed devolution to proceed and gave First Nations without land claim agreements veto power over oil and gas development in traditional territory.
The territorial government is proposing changes to legislation that would remove the veto right the Kaska has on oil and gas development.
Grand Chief Ruth Massie said it's 'unacceptable' that the Yukon government is trying to undermine that agreement by changing the act.
"You know this is a huge infringement on aboriginal rights and titles for one thing, which is still constitutionally protected in this country and the second thing is: it's just plain wrong. And they know it," she said.
Massie said First Nations are willing to sit down and negotiate the issue but added they are also losing patience and are prepared to go the Supreme Court of Canada or the United Nations.
Meanwhile, a lawyer for the Liard First Nation is advising the Yukon Government to back away from amendments to the Oil and Gas Act.
The band’s lawyer said that right is a binding obligation the government can't arbitrarily dispose of.
"Taking this position by a government in Canada, we just find a little bit absurd," said Drew Mildon, a lawyer based in Victoria.
"First Nations should expect to be consulted and appropriately accommodated for developments in their traditional territories. That's not blackmail - that's just paying the landlord his due."
Mildon said the Kaska have a strong case to mount a legal challenge.
"Promises with First Nations have to demonstrate the honour of the Crown. That's something that has to be met, has to be dealt with. It seems like there's really a pretty obvious failure here, it's not really a subtle one."