Michigan Supreme Court Overturns Key Permit for Enbridge Line 5 Pipeline Tunnel Under Straits of Mackinac

Aug 1, 2026

On July 31, 2026, the Michigan Supreme Court ruled 6-1 to vacate the Michigan Public Service Commission's 2023 permit approval for Enbridge's Line 5 pipeline tunnel under the Straits of Mackinac. The court found that regulators failed to evaluate whether the tunnel would extend the 73-year-old pipeline's operational life and harm public trust resources. The decision remands the permit for a new review, adding delays to a project proposed in 2018. Tribal nations celebrated the ruling, while Enbridge expressed disappointment as it awaits further federal permits.

Supreme Court permit reversal

▪The Michigan Supreme Court established a standard requiring courts reviewing agency decisions under the Michigan Environmental Protection Act to independently evaluate compliance rather than deferring to agency conclusions.
▪Justice Brian Zahra dissented from the 6-1 majority, arguing the court improperly expanded the environmental review's scope to include the continued operation of Line 5 itself.
▪On July 31, 2026, the Michigan Supreme Court ruled 6-1 to vacate the Michigan Public Service Commission's December 2023 permit approval for Enbridge's Line 5 pipeline tunnel.
▪The Michigan Supreme Court remanded the permit back to the Michigan Public Service Commission for a new review under the Michigan Environmental Protection Act.

Environmental review inadequacies

▪The Michigan Supreme Court ruled that the Michigan Public Service Commission inconsistently analyzed alternatives by narrowing oil spill risks for Line 5 while broadening them for rail alternatives.
▪The Michigan Supreme Court ruled that the Michigan Public Service Commission failed to determine if the tunnel project would proximately cause the extension of Line 5's operational life.
▪The Michigan Supreme Court found that the Michigan Public Service Commission failed to consider whether the tunnel project would pollute, impair, or destroy public trust resources in the Great Lakes.

Tribal nations legal challenge

▪Tribal nations and environmental groups argued that the tunnel project would turn the Straits of Mackinac, a sacred Anishinaabe site, into a construction zone for over six years.
▪A coalition of four Michigan tribal nations, including the Bay Mills Indian Community, challenged the permit alongside environmental groups like Earthjustice and the Native American Rights Fund.

Tunnel project permit delays

▪Enbridge still requires additional state and federal approvals, including a federal permit from the U.S. Army Corps of Engineers, before construction can begin.
▪The existing Line 5 pipeline continues to transport petroleum through the Straits of Mackinac in defiance of a 2020 shutdown order from Michigan Governor Gretchen Whitmer.
▪The Michigan Supreme Court's ruling adds further delays to the proposed tunnel project, which was originally pitched in 2018 as a four-year, $500 million project to be completed by 2024.

Pipeline spill risk assessment

▪State environmental reviews concluded the tunnel project would cause other harms, including disturbing Native American burial sites, damaging wetlands, and enabling continued fossil fuel reliance.
▪A 2017 state-commissioned report estimated that the existing Line 5 pipeline has a 1-in-60 chance of breaking by the year 2053.
▪Enbridge asserted in a 2018 report that moving the pipeline into an underground tunnel would reduce the oil spill threat to virtually zero.