A proposed $1.5-billion gold and copper mine twice rejected by the federal government was given a new lease on life by B.C. after the company sent a bluntly worded letter to Premier Christy Clark threatening legal action.

Russell Hallbauer, president and chief executive officer of Taseko Mines Ltd., wrote to Ms. Clark on May 13, 2016, demanding the B.C. Environmental Assessment Office proceed with a request to amend the environmental certificate for the New Prosperity project despite Ottawa's repeated rejections.

Amending the certificate would allow Taseko to pursue the project through a narrow process that requires a review of proposed changes only, and not another full environmental assessment.

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Several weeks later, the amendment process was started.

The Taseko letter was released to The Globe and Mail on Tuesday by Independent MLA Vicki Huntington, who obtained it through a Freedom of Information request. She wants to know why Taseko got its certificate so soon after Mr. Hallbauer's letter.

"Does it happen because of the letter and they buckled under with orders from the Premier's office? Or has Taseko been lobbying for the past year or so to get this up and running again and the EAO refused, but is now backing down because of the letter?" she said in an interview.

Ms. Clark's office referred questions to David Karn, a spokesman for the B.C. Ministry of Environment.

"The environmental assessment process in British Columbia is proponent driven, whereby those proposing projects largely determine the timeframes for when they seek review," Mr. Karn said in an e-mail.

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"With respect to this specific matter, the Environmental Assessment Office restarted Taseko's amendment application review following receipt of Taseko's May, 2016, request. Until receiving this letter, EAO had not received any communication from Taseko for over a year."

Taseko did not respond to requests for comment.

Mr. Hallbauer's letter makes it clear he is tired of waiting.

"Premier – I hope it is clear that this Company and its shareholders cannot simply sit back and allow our project to be placed on ice by regulators, or to be unfairly treated by agreements with First Nations that affect our interests without any consultation with us," he wrote.

He said both federal and provincial government officials treated the company unfairly, and reminded Ms. Clark of a case that cost the government about $150-million in 1999 after B.C. Supreme Court ruled the province illegally cancelled a timber-harvesting licence.

"I have personally been involved in mineral development around the world and have experienced subversive undermining by government employees of important projects. I cannot believe, as a Canadian that the same could hold true in Canada," Mr. Hallbauer's letter states. "It indeed though happens, everyone in this Province should remember Carrier Lumber, one of the more egregious efforts of the state and bureaucracy to destroy a business."

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Mr. Hallbauer wrote that during the federal environmental review, where federal officials "met secretly" with members of the Tsilhqot'in National Government, which opposed the project.

Taseko, which has spent more than $130-million trying to develop the mine, initially won approval from the B.C. government, but in 2010, the Prosperity project, as it was then called, failed to pass federal environmental reviews. In 2014, a revised project known as New Prosperity again failed to get federal authorization.

Mr. Hallbauer also says B.C. officials "were actively working to discredit our new plan with the [federal] panel."

Mr. Hallbauer wrote that if the province did not grant an amended environmental certificate, the government should buy the New Prosperity mineral tenures or Taseko would go to court seeking damages "based upon a claim of de facto expropriation, among other things."

Taseko filed just such a claim against the federal government in B.C. Supreme Court last February. The case has yet to be heard.

In June, much to the surprise of the Tsilhqot'in National Government, which has long opposed the mine, the province started the process to amend the project's environmental certificate, giving the company another chance to try to get through the environmental review process.