TORONTO - Ontario aboriginals will use "any means necessary" to protect their treaty rights against the province's new land development legislation, First Nations leaders warned Monday.

A showdown is looming over the Far North Act, they warned, which is slated for final reading in the legislature later this week.

"If Bill 191 is passed, if it's forced through, there will be conflict in the north," said Stan Beardy, grand chief of the Nishnawbe Aski Nation.

The political organization -- which represents 49 First Nations -- said the legislation robs aboriginals of their treaty rights and doesn't give them a say in how their lands will be developed.

First Nations support community-based land planning, but don't like the fact the act gives the government veto power, said Beardy.

"It imposes a massive, interconnected protected area over our homelands without compensation and without our consent," he said.

"We will oppose it by any means necessary. There will be no certainty for the government or for investors."

The bill would lock up to 42 per cent of Ontario's land mass from development, protecting 225,000 square kilometres of boreal forest.

Several chiefs echoed Beardy's comments at a news conference at the Ontario legislature, where they accused Premier Dalton McGuinty of failing to keep his promise not to pass the act without their approval.

"When (McGuinty) met with us a year ago, the one brief time he met with us, he said: 'this bill will not go forward until First Nations support it,' but today he wants to move it forward," said Chief Stan Loutit.

"He lied back then and that is not right for a government leader to do."

McGuinty ducked questions in the legislature Monday on the opposition to the bill from aboriginals and many municipalities in the north, deflecting queries to Natural Resources Minister Linda Jeffrey.

The province changed the legislation to address the First Nations' concerns about the ministry's so-called veto power, said Jeffrey.

"We have completely re-ordered the approval process so that all of the approvals that the minister would make would be at the beginning and the final approval would be for the First Nations community at the end of the process," she said.

"This is a pretty dramatic, historic change to the way we're going about doing legislation."

However, the changes aren't good enough and the bill must be killed, said Beardy.

"Ontarians don't want more fights with First Nations, they don't want more First Nation leaders put in jail, they don't want more lawsuits, but this is where McGuinty is heading if he tries to force this bill on us," he said.

"We have read the revised bill and we're still opposed to it."

The opposition parties complained about the lack of consultation on the bill.

New Democrat Gilles Bisson, who represents the huge northern riding of Timmins-James Bay, said there is not one First Nation in the north that wants the legislation as it stands.