The Assembly of First Nations chiefs, a national Aboriginal body, has joined the Tsilhqot'in Nation in opposing Taseko Mine's revamped proposal to build the $1-billion Prosperity gold and copper mine in Central B.C.

The chiefs made the decision at the three-day Assembly of First Nations' (AFN) Chiefs-in-Assembly in Moncton, N.B., which wrapped up this week.

The chiefs' resolution issues a caution to the federal and provincial governments that proceeding with a review of the revamped plan would demonstrate "utter disregard for the survival of First Nations as distinctive cultures within Canada and it would ignore the recent commitment to the United Nations Declaration on the Rights of Indigenous Peoples."

The Tsilhqot'in welcomed the support.

“The renewed support of the AFN gives us the confidence that we are on the right track," said chief Joe Alphonse, tribal chair of the Tsilhqot'in Nation.

"As indigenous peoples, it’s not always about economics, but about the environment that we live with," said Alphonse.

The Tsilhqot'in Nation had strongly rejected Taseko's revised plan just days after the company filed the revamped plan with the federal government in early June, which no longer called for the destruction of Fish Lake.

The details of the new plan won't be released until the federal government ensures the proposal is adequate, although the Tsilhqot'in received a copy the same day as it was filed with the federal government.

The Tsilhqot'in say the integrity of Fish Lake (called Teztan Biny in the Tsilhqot'in language) and its surrounding environment are not saved by simply not using the lake for mine waste storage.

The original plan called for the lake to be drained and used a storage area for waste rock and dirt. The waste rock will now be trucked to another area.

Taseko's revised plan adds $300 million in costs to the mine, which had an original price tag of $800 million.

The company says it was able to finance the additional cost because long-term consensus gold and copper prices have gone up significantly.

The company has said it remains hopeful that First Nations will talk to them about the revised project.

Last year, a federal panel concluded there would be significant adverse environmental effects from the Prosperity mine on fish and fish habitat, traditional First Nations use and on potential, or established, Aboriginal rights or title. The most contentious issue surrounding the project was the use of Fish Lake, which the panel estimated would destroy 90,000 rainbow trout.

Last November, the federal government delivered its rejection of Prosperity.

However, the federal government noted that the project had been rejected "as proposed," opening up the door to a redesigned project.

The B.C. Liberal government had been pressing the federal government to approve the project, arguing the economic benefits and jobs produced by the mine outweigh environmental impacts identified in a federal review.

B.C. Premier Christy Clark has been a proponent of the Prosperity mine moving ahead.