July 31, 2026.
LANSING — The Michigan Supreme Court vacated the Michigan Public Service Commission's (PSC) approval of Enbridge Energy's proposed Line 5 tunnel beneath the Straits of Mackinac, ruling that state regulators failed to fully evaluate the project's environmental impacts under the Michigan Environmental Protection Act (MEPA).
In a sweeping opinion issued July 31, the court reversed the Michigan Court of Appeals, vacated the PSC's 2023 approval of the project, and remanded the case to the commission for a new review that must address broader environmental and public trust concerns.
The ruling represents a major victory for several Michigan Tribal Nations and environmental organizations that challenged the PSC's approval, including the Sault Tribe, Bay Mills Indian Community, Little Traverse Bay Bands of Odawa Indians, Grand Traverse Band of Ottawa and Chippewa Indians, Nottawaseppi Huron Band of the Potawatomi, Environmental Law & Policy Center, Michigan Climate Action Network, and For Love of Water.
Court: PSC's Review Was Too Narrow.
At the heart of the case was whether the PSC improperly limited its environmental review solely to the proposed four-mile tunnel replacement beneath the Straits instead of considering whether the project would effectively extend the operational life of the entire 645-mile Line 5 pipeline.
Justice Elizabeth Welch, writing for the majority, concluded that the PSC's analysis was legally insufficient.
The court held that MEPA requires regulators to examine:
- Whether the tunnel project will factually and proximately extend the life of Line 5 and the environmental impacts resulting from that extension.
- Whether alternatives were compared using a consistent environmental standard.
- Whether the project affects public trust resources protected under Michigan law.
The justices ruled the PSC should have evaluated whether constructing the tunnel would enable continued operation of Line 5 and the environmental consequences that could follow.
New Standard for Environmental Reviews.
The decision establishes significant precedent for environmental reviews conducted by Michigan agencies.
The Supreme Court held that courts reviewing agency decisions under MEPA must independently examine environmental issues rather than defer to agency conclusions.
According to the opinion, judicial review of MEPA determinations must be conducted de novo, meaning courts independently evaluate the legal and factual issues rather than simply determining whether the agency acted reasonably.
The court also concluded the PSC acted inconsistently by considering greenhouse gas emissions associated with products transported through Line 5 while refusing to consider other environmental risks, including the possibility of oil spills resulting from continued pipeline operations.
Public Trust Doctrine Must Be Considered.
Another major aspect of the ruling concerns Michigan's long-standing public trust doctrine.
The Supreme Court found the PSC erred by failing to evaluate how the project could affect public trust resources, including the Great Lakes, which Michigan holds in trust for public uses such as fishing, boating, hunting, and navigation.
The court stated that MEPA requires separate consideration of impacts to these protected public resources and that the PSC must address those issues on remand.
Background of the Project.
Enbridge's proposal would replace the aging dual Line 5 pipelines resting on the bottom of the Straits of Mackinac with a new 30-inch pipeline housed inside a concrete-lined tunnel drilled beneath the lakebed.
The tunnel project emerged from agreements negotiated between Enbridge and the State of Michigan beginning in 2017 and would eventually lead to decommissioning the existing underwater pipelines. Once completed, the Mackinac Straits Corridor Authority would own the tunnel and lease it back to Enbridge for 99 years.
Supporters argue the tunnel would greatly reduce the risk of an oil spill in the Straits while maintaining fuel supplies to Michigan, the Upper Peninsula, and Ontario.
Opponents have maintained that the project would prolong operation of Line 5 for decades and therefore required a much broader environmental review.
Tribal Nations Challenged Approval.
The participating Tribal Nations argued throughout the proceedings that the PSC should have considered impacts beyond the tunnel itself, including continued operation of the pipeline and its potential effects on treaty-protected waters and natural resources.
The Supreme Court noted that the Great Lakes and the Straits of Mackinac hold profound ecological, cultural, and historical significance, particularly for the Tribal Nations involved in the litigation.
Dissent.
Justice Brian Zahra agreed only that the case should be returned to the PSC to expressly consider the public trust doctrine.
However, he disagreed with the majority's broader interpretation of MEPA, arguing that the PSC's environmental review should remain focused on the replacement tunnel rather than the entire Line 5 system. He also argued courts should continue giving deference to agency expertise when reviewing administrative decisions.
What Happens Next.
The ruling does not cancel the proposed tunnel project.
Instead, it vacates the PSC's approval and sends the case back to the commission, which must conduct additional proceedings consistent with the Supreme Court's opinion before deciding whether the project can be approved under Michigan law.
The decision is expected to influence not only the future of the Line 5 tunnel proposal but also how Michigan agencies evaluate environmental impacts in major infrastructure projects under the Michigan Environmental Protection Act.
Sault Tribe Guardian Advertising Below. Click here for more information.
