Nov 23 (Reuters) – Two western Canadian provinces that are seeking more autonomy from Ottawa, popular moves with their conservative supporters, have run into fierce opposition from indigenous First Nations who vow to challenge any legislation with court action or protests.

Conservative-led governments in oil-producing Alberta and Saskatchewan are demanding Liberal Prime Minister Justin Trudeau’s government cede more power on issues from climate policy to gun control.

However, large parts of Canada, a constitutional monarchy with England’s King Charles as nominal head of state, are covered by historic treaties between the British Crown and First Nations, semi-autonomous indigenous groups who exercise some control over their own lands.

The federal government’s authority is being challenged in Alberta, where Danielle Smith became premier last month after promising to introduce the Alberta Sovereignty Act, which would allow the provincial government to ignore federal laws it does not like.

Saskatchewan’s Premier Scott Moe introduced similar legislation this month to assert its control over its natural resources, including crude, potash and uranium

But First Nation chiefs are pushing back in a coordinated show of opposition that echoes indigenous resistance to Quebec’s independence movement three decades ago.

“If the province goes ahead with the Sovereignty Act, I guarantee there will be nothing but litigation over this for the next 50 years,” Chief Allan Adam of Athabasca Chipewyan First Nation in Alberta said.

All Alberta First Nations chiefs released a joint statement last week rejecting the Sovereignty Act, saying it falsely assumes Alberta holds legal title to First Nation lands.

Alberta’s proposed legislation “undermines the authority and duty of the sovereign nations that entered into treaty,” Treaty 8 First Nations Grand Chief Arthur Noskey said in the statement.

First Nations only agreed in treaties to share their land to “the depth of a plow,” said Chief Bobby Cameron of Saskatchewan’s Federation of Sovereign Indigenous Nations, meaning agreements did not cover oil or minerals deeper underground.

“Whether we see this through in court or on the land, our people are ready to defend and protect our lands and waters as we see fit,” he said. “If our grassroots members want to put up blockades, then that’s what we’ll do.”

Athabasca Chipewyan’s Adam said the federal government funds First Nations services such as health and schooling, and indigenous people are also concerned the Alberta government could remove environmental protections around resource extraction.

Alberta officials, including the premier, aim to meet with chiefs and the legislation will not abrogate existing treaty rights, said government spokesperson Rebecca Polak.

Saskatchewan’s legislation does not detract from treaty rights, the province’s Justice Minister Bronwyn Eyre said, noting it was aimed at asserting its authority over resources and creating a tribunal to estimate economic damages from federal regulations.

Those could include new federal rules to cut emissions from fuel, power generation and oil production, laying the groundwork for possible legal challenges by Saskatchewan, she said.

“We feel we’re on very solid legal footing,” Eyre said.

First Nations opposed to the sovereignty legislation would also have a strong legal argument because their relationship is with the Crown, not the provinces, said Kathy Brock, a politics professor at Queen’s University in Kingston, Ontario.

The backlash against Alberta and Saskatchewan sovereignty mirrors Indigenous opposition to Quebec’s attempt to secede from Canada in a 1995 referendum which it narrowly lost.

“When we had the referendum in Quebec First Nations people voted in the 90s (percent) against separating and being taken out of Canada,” Brock said. “This was a very big issue.”