The Michigan Supreme Court waded into one of the state’s most closely watched energy fights yesterday, hearing arguments over whether regulators got it right when they approved Enbridge’s plan to reroute a section of the Line 5 oil pipeline into a concrete tunnel beneath the Straits of Mackinac. Tribal nations and environmental groups urged the justices to toss the permit or send it back for more scrutiny, while Enbridge argued the tunnel is the safest way to get an aging pipeline out of open water.
State regulators signed off on the siting permit on Dec. 1, 2023, concluding that the roughly four-mile tunnel would replace the dual 20-inch pipes with a single 30-inch line housed inside a 21-foot concrete-lined tunnel routed through bedrock beneath the lakebed. According to the Michigan Public Service Commission, Line 5 runs about 645 miles and carries roughly 540,000 barrels a day. The MPSC conditioned its approval on Enbridge securing remaining federal and state permits and required a detailed risk management plan along with a list of safety and inspection measures before construction can start.
The permit is under fire from four tribal nations, Flow Water Advocates, and allied environmental groups, who argue the commission’s review glossed over feasible alternatives, treaty and public trust harms, and the pipeline’s broader environmental footprint. As reported by Michigan Advance, the appeals landed at the state’s high court after the Court of Appeals in 2025 declined to disturb the MPSC ruling. The challengers want the Supreme Court to either remand the permit to the commission for a more robust review or vacate it altogether.
Enbridge attorney John Bursch pressed the justices to leave the permit in place, framing the choice as keeping the current pipeline in the water or moving it into the tunnel. “Where do you want the pipeline? Do you want it in the tunnel or do you want it operating in the water?” he asked, according to Bridge Michigan. Bursch also told reporters the company would have loved to have started it five years ago, a remark captured by Michigan Public Radio after the hearing.
Opponents countered that both the federal review and the state permit process sidestepped key questions about cultural impacts, wetlands loss, and alternatives that would remove oil shipments from the Great Lakes entirely. Julie Goodwin of Earthjustice argued that the U.S. Army Corps’ final environmental impact statement “sets up a predetermined decision to approve the tunnel,” according to reporting by WCMU. Tribal governments have also warned that the planned tunnel route would cut through places they view as culturally and spiritually significant.
Legal stakes and timeline
The tunnel fight is unfolding alongside a string of federal rulings that could reshape the broader Line 5 battle. In December, a federal judge held that federal pipeline law limits Michigan’s authority to order a shutdown, a ruling reported by AP News. Then, in February, the U.S. Supreme Court heard procedural arguments over whether Michigan Attorney General Dana Nessel’s separate Line 5 lawsuit belongs in state or federal court, as Michigan Advance reported. In the tunnel case, the Michigan Supreme Court could send the permit back for more fact-finding or allow construction to proceed if Enbridge clears the remaining permitting hurdles.
Whatever the outcome, the decision will reverberate well beyond the courtroom. The ruling will help determine how much power state regulators have over major energy infrastructure, how treaty rights and public trust obligations factor into that oversight, and whether the long-contested tunnel project actually gets built.
What’s next
Even if the Michigan Supreme Court lets the siting permit stand, Enbridge still needs a federal permit from the U.S. Army Corps of Engineers and additional state approvals from the Department of Environment, Great Lakes, and Energy before it can break ground, consistent with the MPSC order. The Army Corps released its final environmental impact statement in February and began a 30-day waiting period before issuing a record of decision, according to WCMU. Any remand to the commission or new round of appeals would likely stretch the timetable by months or even years, advocates and industry lawyers warned.
The case hits especially close to home for northern Michigan. Regulators and industry analysts say Line 5 carries propane and other products that heat homes and fuel businesses across the region, and they estimate that shutting down the straits segment with no replacement in place would require a major shift to truck and rail transport. Enbridge’s project materials and state filings have leaned heavily on those fuel security arguments in asserting that the tunnel is the safest long-term solution. That trade-off, environmental risk versus energy reliability, is what the court now has to sort through.
After a day of pointed questioning from the justices, neither side emerged from the Lansing courthouse with a clear read on how the panel will rule. The Michigan Supreme Court could take months to issue an opinion that will decide whether the proposed tunnel, the state’s regulatory process, or both move forward.
