The Minnesota Supreme Court will not review a lower court's decision to affirm state utility regulators' approval of Enbridge's controversial new oil pipeline across northern Minnesota — a blow to opponents of Line 3.

The high court on Wednesday rejected a petition by pipeline opponents that sought to overturn a June decision by the Minnesota Court of Appeals.

The appellate court — by a 2-1 vote — upheld the Minnesota Public Utilities Commission's (PUC) 2020 final approval of the 340-mile oil pipeline that will replace Enbridge's current Line 3, which is corroding and can operate at only 51 % capacity.

The $3 billion-plus new pipeline, which will transport oil from Canada, is more than 90% built. Calgary, Alberta-based Enbridge plans to begin shipping crude on it during the fourth quarter.

"The rights of a Canadian corporation continue to prevail over the laws of nature and the human rights of Anishinaabe people," Winona LaDuke, head of the Indigenous environmental group Honor the Earth, said after the high court's decision. "It's a sad day for Minnesota."

Enbridge said it's "pleased with the decision from the Minnesota Supreme Court," and that the project has been "reaffirmed multiple times by the Minnesota Public Utilities Commission and this June by the Minnesota Court of Appeals."

In July, Honor the Earth and other environmental and climate groups, along with the White Earth and Red Lake bands of Ojibwe, petitioned the Supreme Court to hear the case.

The state Supreme Court usually hears fewer than 15% of the petitions it receives.

The environmental groups, tribes and the Minnesota Department of Commerce had all appealed the PUC's decision to approve the pipeline.

They made several legal arguments, but the core complaint focused on the adequacy of Enbridge's long-term oil demand forecast, which the PUC accepted when it approved the new Line 3.

The Department of Commerce did not join in the petition to the Supreme Court.

Enbridge says the new Line 3, built partly along a new route, will be safer and restore the full flow of oil. Pipeline opponents say it will expose new regions of lakes, rivers and wild rice waters to oil-spill degradation and will exacerbate climate change.