State’s highest court says regulators failed to fully examine environmental and public trust issues before approving Enbridge project beneath the Straits of Mackinac

LANSING – Michigan’s highest court on Friday handed both a victory to Native American tribes and environmental groups—and another setback to one of the Midwest’s most closely watched energy infrastructure projects.

In a 6-1 decision, the Michigan Supreme Court ruled that the Michigan Public Service Commission (MPSC) failed to fully consider environmental and public trust issues before approving Enbridge’s permit to build a tunnel beneath the Straits of Mackinac to house the Line 5 oil pipeline.

The ruling sends the permit back to the MPSC for further review, creating new uncertainty over a project supporters say is critical to protecting regional energy supplies while opponents argue it could prolong the risk of a catastrophic oil spill in the Great Lakes.

The decision does not shut down Line 5 or permanently reject the proposed tunnel. Instead, the court concluded state regulators did not adequately analyze key issues before issuing the permit, including whether the project would effectively extend the operating life of the 73-year-old pipeline, what additional environmental impacts that could create, and whether Michigan’s obligation to protect public trust resources in the Great Lakes had been fully considered.

For Michigan businesses, manufacturers and consumers, the ruling means another delay for a multibillion-dollar infrastructure project that has spent nearly a decade navigating state and federal permitting, environmental reviews and court challenges.

Why Line 5 Matters

Line 5 transports crude oil and natural gas liquids from Superior, Wisconsin, through Michigan before crossing beneath the Straits of Mackinac and continuing into Ontario.

The pipeline supplies crude oil to refineries that produce gasoline, diesel and jet fuel used throughout the Great Lakes region. It also delivers natural gas liquids used to produce propane, an important heating fuel for many homes and businesses in Michigan’s Upper Peninsula.

Supporters of the tunnel project—including Enbridge, business organizations and many labor unions—argue replacing the section of pipeline resting on the lakebed with one housed inside a concrete-lined tunnel drilled through bedrock would dramatically reduce the risk of an oil spill while preserving a critical regional energy corridor.

Supporters also say the project would create hundreds of construction jobs while improving the long-term reliability of fuel supplies for Michigan, neighboring states and parts of Canada.

Why Tribes And Environmental Groups Opposed The Permit

The legal challenge was brought by Native American tribes and environmental organizations that argue the greatest threat is the possibility of a rupture beneath the Straits of Mackinac, where powerful currents could rapidly spread oil into both Lakes Michigan and Huron.

The tribes contend a major spill could contaminate drinking water, damage one of the world’s largest freshwater ecosystems, devastate commercial and tribal fisheries, hurt tourism, and threaten treaty-protected fishing rights that have existed for generations.

Environmental groups have also argued the tunnel would extend the life of a pipeline originally built in 1953, prolonging reliance on fossil fuels while increasing long-term environmental risks.

Enbridge strongly disputes those claims. The company says the tunnel project is specifically designed to reduce environmental risk by enclosing a replacement pipeline inside a reinforced concrete tunnel bored through bedrock beneath the lakebed, protecting both the pipeline and the Great Lakes from vessel strikes and other hazards.

Importantly, the Michigan Supreme Court did not rule that the tunnel itself would cause environmental damage. Instead, the justices concluded the Michigan Public Service Commission did not adequately evaluate those concerns before granting the permit.

Court Orders New Review

The Supreme Court directed the MPSC to reconsider the permit using a more thorough analysis of environmental impacts and the state’s public trust responsibilities.

That means regulators must again weigh the project’s potential benefits—including improved pipeline protection, construction jobs and continued energy reliability—against concerns raised by tribes and environmental advocates.

Enbridge said it is reviewing the Michigan Supreme Court’s decision and considering its legal options. Attorneys representing the tribes welcomed the ruling, saying regulators must give greater consideration to the potential impacts on the Great Lakes and treaty-protected resources. Additional reaction from both sides is expected in the coming days.

The ruling represents another chapter in one of Michigan’s longest-running infrastructure battles. Separate lawsuits involving Line 5 remain pending in both state and federal courts, meaning Friday’s decision is unlikely to be the final word on the project’s future.

What Happens Next

The case now returns to the Michigan Public Service Commission, where regulators could conduct additional hearings, require further environmental analysis or again approve the permit after addressing the deficiencies identified by the Supreme Court.

Line 5 remains in operation while the legal and regulatory process continues. The Supreme Court’s ruling affects the proposed tunnel project, not the operation of the existing pipeline.

For Michigan residents, businesses and policymakers, the debate extends well beyond a single pipeline. It highlights the increasingly difficult balance between maintaining reliable and affordable energy supplies, creating construction jobs and protecting the Great Lakes—one of the state’s most valuable natural and economic resources.

Friday’s ruling does not end the Line 5 debate—it simply sends one of Michigan’s most controversial infrastructure projects back to regulators. The ultimate decision will shape more than the future of a single pipeline. It could influence how Michigan balances economic development, energy reliability and environmental protection for major infrastructure projects for years to come.