WASHINGTON — The U.S. Supreme Court on Wednesday ruled unanimously that Michigan's lawsuit seeking to shut down a section of an aging pipeline beneath a Great Lakes channel will remain in state court. Justice Sonia Sotomayor wrote for the court that Enbridge waited too long to try to move the case to federal court.

Michigan Attorney General Dana Nessel sued in state court in June 2019, seeking to void the easement that allows Enbridge to operate a 4.5-mile section of Line 5 under the Straits of Mackinac. The pipeline has moved crude oil and natural gas liquids between Superior, Wisconsin, and Sarnia, Ontario, since 1953.

In June 2020, Ingham County Judge James Jamo issued a restraining order shutting down the pipeline. Enbridge was allowed to continue operations after meeting safety requirements. The company moved the lawsuit into federal court in 2021, arguing that the case affected U.S. and Canadian trade.

In June 2024, a three-judge panel of the 6th U.S. Circuit Court of Appeals sent the case back to Jamo, finding that Enbridge missed a 30-day deadline to change jurisdictions.

Earlier concerns about the pipeline's condition had accumulated over several years. In 2017, Enbridge engineers revealed they had known about gaps in the protective coating of the pipeline section since 2014. A boat anchor damaged the section under the Straits of Mackinac in 2018.

In 2020, the Michigan Department of Natural Resources under Governor Gretchen Whitmer revoked the easement for Line 5 under the Straits of Mackinac. Enbridge filed a separate federal lawsuit challenging the revocation, and a federal judge ruled in favor of the company, blocking the revocation. That judge decided that federal regulators, not the state, are responsible for Line 5 safety, and that federal regulators had found no issues that would warrant shutting down the line.

Whitmer appealed that ruling to the 6th U.S. Circuit Court of Appeals. In March 2026, the Supreme Court rejected her appeal that she could not be sued in federal court.

Enbridge is also seeking permits to encase the pipeline section under the Straits of Mackinac in a protective tunnel. In 2023, the Michigan Public Service Commission granted permits for the project. A coalition of environmental groups and Michigan tribes filed a lawsuit seeking to void the state permits, and the Michigan Supreme Court is weighing that case. Enbridge also needs approval from the U.S. Army Corps of Engineers and the Michigan Department of Environment, Great Lakes and Energy.

In summer 2025, a federal judge in Madison gave Enbridge three years to shut down part of Line 5 that runs across the Bad River Band of Lake Superior's reservation. The company appealed the shutdown order to the 7th U.S. Circuit Court of Appeals, and in February 2026 started work to reroute the line around the reservation. The Bad River Band and environmental groups filed a pending state lawsuit seeking to halt the reroute construction work.