Faced with a decision that would inevitably irritate one key constituency of his own DFL Party, Gov. Tim Walz chose to challenge Enbridge's controversial $2.6 billion pipeline project after state utility regulators approved it for a second time.

As expected, environmental groups cheered the decision to appeal the replacement for Enbridge's deteriorating Line 3.

Building trades unions panned the decision.

"When it comes to any project that impacts our environment and our economy, we must follow the process, the law, and the science," Walz said in a statement. "The Department of Commerce's appeal is a part of that process."

The Minnesota Department of Commerce on Wednesday asked the courts to overturn the project's approval by the Public Utilities Commission (PUC).

Two Ojibwe bands and four environmental groups filed similar challenges with the Minnesota Court of Appeals.

Enbridge, based in Calgary, Alberta, said in a statement that the appeal "is not supported by evidence or Minnesota law" and pursues an argument that has failed numerous times in the regulatory process.

The project would be one of the largest construction projects in recent Minnesota history. Enbridge said it would employ more than 4,000 at its peak.

Unions criticized the state's appeal for further complicating the long-delayed project.

"We are frustrated because we feel this is a distraction from all kinds of other work that really needs to be done," said Kevin Pranis, Minnesota and North Dakota marketing manager for the Laborers' union.

Minnesota Republican leaders also slammed the Commerce Department appeal, saying the northern Minnesota economy needs the jobs. Meanwhile, 17 DFL legislators sent a letter praising Walz's decision.

However, pipeline opponents reiterated their positions that the project could be a potential environmental disaster.

"It shows the state recognizes the economic and financial risks of this pipeline project," said Winona LaDuke, director of Honor the Earth, a Minnesota-based Indigenous environmental group.

The PUC in June 2018 first approved the pipeline across northern Minnesota. The appeals court sent the project back to the PUC, ruling that the environmental impact statement (EIS) neglected to address certain areas. The PUC approved the updated EIS and reapproved the pipeline in February.

The Commerce Department contends that the PUC committed a "legal error" in its evaluation of the accuracy of Enbridge's long-term oil demand forecast because the company never submitted a proper forecast.

Also, the department said the PUC shifted the burden of proof from Enbridge to the department itself to show that long-term oil demand would decrease.

The Commerce Department serves as a research arm for the PUC, and also represents the public interest before the commission.

The department has contended since 2017 that there isn't enough long-term oil demand to merit a new Line 3, which would transport Canadian oil to Superior, Wis. Enbridge said it submitted a valid oil-demand forecast that was accepted by the PUC.

Court appeals filed by pipeline opponents also have challenged the PUC on oil-demand forecasts, as well as a host of other factors, including the effect of the coronavirus-induced implosion of the Canadian oil industry.

A joint appeal was filed by Honor the Earth, the Sierra Club and the Red Lake and White Earth bands of Ojibwe. Friends of the Headwaters, a Minnesota environmental group, and Youth Climate Intervenors also appealed the PUC's February re-approval of the environmental impact statement for Line 3. The new Line 3 would replace an existing pipeline that is deteriorating.

Enbridge said the new pipeline would be safer and restore the full flow of oil, while opponents say oil spills could foul a new region of Minnesota's lake country and contribute to climate change.

Line 3 has been winding through the state's regulatory process for about six years, and Enbridge still must get permits for the project from state agencies and the U.S. Army Corps of Engineers.