Ontario’s cancellation of a proposed wind farm in the St. Lawrence River could cost Canada $568 million, if a NAFTA tribunal rules in favour of a U.S.-based energy company.

Hearings began in Toronto this week into the case of U.S.-based Windstream Energy. The company launched a lawsuit against Ontario in 2012, after the province cancelled an offshore wind farm project the company wanted to build off Wolf Island, in the St. Lawrence River near Kingston.

The federal government is the defendant in cases brought under NAFTA, even in instances where provincial policy is at issue.

The initial filing sought C$475 million in damages for the cancellation of the 100-turbine project, but according to a recent report in the Globe and Mail, the company is now seeking $568 million.

Ontario placed a moratorium on offshore wind farms in 2011, cancelling dozens of projects. But Windstream says that, unlike other projects, it had a contract with the Ontario Power Authority, according to a 2012 Toronto Star report.

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Windstream says it placed a $6-million security with the power authority, and had signed a supply contract with Siemens Canada before the province enacted the moratorium.

“Although we view litigation as an absolute last resort, we have been given no other option but to pursue this path,” Windstream president Ian Baines said at the time, as quoted at the Star.

“We hope that this mechanism will break the provincial political interference.”