The oil company behind Line 5 lost a major procedural battle Wednesday as the Supreme Court said Michigan’s lawsuit can remain in state court. The ruling does not settle the pipeline’s future, but it preserves a case that could shape whether a 4. 5-mile section beneath the Straits of Mackinac keeps operating. For Michigan, the decision keeps pressure on a project tied to energy transport, environmental risk, and a dispute that has already stretched across multiple courts and jurisdictions.
Why the Line 5 case still matters
The case centers on a section of the Line 5 energy pipeline beneath a Great Lakes channel linking Lake Michigan and Lake Huron. Line 5 has moved crude oil and natural gas liquids between Superior, Wisconsin, and Sarnia, Ontario, since 1953. The legal fight intensified when Dana Nessel, Michigan’s attorney general, sued in state court in June 2019 to void the easement that allows the oil company to operate the underwater section.
That challenge quickly became more than a local dispute. In June 2020, Ingham County Judge James Jamo granted a restraining order shutting down the pipeline, though the oil company was allowed to continue operating after meeting safety requirements. Later, the company moved the lawsuit into federal court in 2021, arguing that the matter touches US and Canadian trade. A three-judge panel of the Sixth US Circuit Court of Appeals sent the case back to state court in June 2024, finding the company missed a 30-day deadline to change jurisdictions.
What the Supreme Court decided
Justice Sonia Sotomayor wrote for a unanimous court that the oil company waited too long to try to move the case into federal court. That narrow ruling matters because it keeps the state-level challenge alive, rather than letting the dispute shift to a federal forum where the company had hoped to fight it.
The decision also leaves the broader Line 5 conflict unresolved. The pipeline remains at the center of overlapping legal battles in Michigan, Wisconsin, and federal court. In Michigan, the Department of Natural Resources under Governor Gretchen Whitmer revoked the Straits easement for Line 5 in 2020, and the company filed a separate federal lawsuit challenging that move. A federal judge blocked the revocation, and Whitmer has appealed to the Sixth US Circuit Court of Appeals. In March, the Supreme Court rejected Whitmer’s appeal arguing she could not be sued in federal court.
Environmental risk, permits, and tunnel plans
At the core of the dispute is the fear that the section beneath the straits could rupture and cause a catastrophic spill. Those concerns have grown since 2017, when engineers revealed that gaps in the section’s protective coating had been known since 2014. A boat anchor damaged the section in 2018, adding to the sense of urgency surrounding the pipeline’s condition.
The oil company is also seeking permits to encase the underwater section in a protective tunnel. The Michigan Public Service Commission granted the relevant permits in 2023, but a coalition of environmental groups and Michigan tribes has filed a lawsuit seeking to void the state permits. The state supreme court is weighing that case. Separate approvals are still needed from the US Army Corps of Engineers and the Michigan Department of Environment, Great Lakes and Energy.
Regional consequences beyond Michigan
The legal stakes extend well beyond one state. In Wisconsin, a federal judge in Madison last summer gave the oil company three years to shut down part of Line 5 that runs across the Bad River Band of Lake Superior’s reservation. The company has appealed that order to the Seventh US Circuit Court of Appeals, while also beginning work in February to reroute the line around the reservation.
The Bad River Band and environmental groups have filed a state lawsuit seeking to halt the reroute, adding another layer to a dispute that now spans courts, states, and regulatory agencies. For the oil company, the Supreme Court’s decision is a setback because it keeps Michigan’s case moving in a venue that has already proved difficult. For Michigan, it preserves a pathway to press its challenge over Line 5 without delay.
What happens next will depend on the pace of the state case, the tunnel litigation, and the separate federal appeals. For now, the Supreme Court has left the key question intact: how long can the oil company keep Line 5 operating under the Straits of Mackinac while courts decide its fate?
