The Supreme Court ruled unanimously Wednesday that Michigan's lawsuit seeking to shut down a section of an aging pipeline beneath a Great Lakes channel will remain in state court rather than move to federal jurisdiction.

Justice Sonia Sotomayor wrote for the court that Enbridge energy company waited too long to attempt moving the case to federal court, missing required deadlines for changing jurisdictions.

The dispute centers on Line 5, a pipeline that has transported crude oil and natural gas liquids between Superior, Wisconsin, and Sarnia, Ontario, since 1953. Michigan Attorney General Dana Nessel filed suit in state court in June 2019 seeking to void the easement allowing Enbridge to operate a 4.5-mile section under the Straits of Mackinac, which connect Lake Michigan and Lake Huron.

Environmental concerns over the pipeline section have intensified since 2017, when Enbridge engineers revealed they had known about gaps in the protective coating since 2014. A boat anchor damaged the section in 2018, further raising fears of a potential spill. In 2020, Michigan's Department of Natural Resources revoked the straits easement for Line 5.

Enbridge moved the lawsuit to federal court in 2021, arguing the case affects U.S.-Canadian trade relations. However, a three-judge panel from the 6th U.S. Circuit Court of Appeals returned the case to state court in June 2024, finding the company had missed the 30-day deadline to change jurisdictions.

The company is currently seeking permits to encase the pipeline section in a protective tunnel beneath the straits. While Michigan's Public Service Commission granted relevant permits in 2023, Enbridge still requires approval from the U.S. Army Corps of Engineers and Michigan's Department of Environment, Great Lakes and Energy. The pipeline also faces legal challenges in Wisconsin, where a federal judge ordered Enbridge to shut down part of Line 5 running across the Bad River Band reservation within three years.