Michigan wins key legal battle over Line 5 pipeline

Michigan’s decades-long fight to shut down the Line 5 pipeline will be heard in state court after the U.S. Supreme Court unanimously ruled that the dispute belongs there, clearing the way for judges to weigh whether the aging oil pipeline can continue crossing the Straits of Mackinac. 

The ruling is seen as a win for tribes, environmentalists, and state Attorney General Dana Nessel, who preferred to keep the fight in state court. She has since 2019 been trying to revoke the easement that allows the pipeline to cross the Straits, which connect lakes Michigan and Huron, citing the risk of an oil spill.

“For far too long, following years of Enbridge’s delay tactics, the fear of a catastrophic spill from Line 5 has haunted our state, threatening to turn our most vital natural resource into a man-made disaster,” Nessel said in a statement.

The pipeline, owned by the Canadian company Enbridge Energy, transports crude oil and natural gas liquids 645 miles from Superior, Wisconsin, to Sarnia, Ontario, a route that includes a critical 4.5-mile segment along the lakebed of the Straits.

Writing for a unanimous court, Justice Sonia Sotomayor said Enbridge waited too long to move the case to federal court and that the company’s “counterarguments are not persuasive.” 

Legal experts said the procedural ruling was significant because it determines which court will decide the pipeline’s future. Enbridge’s lawyers argued that a federal court was the proper venue because federal safety laws and international agreements are involved. (The Canadian government opposes shutting down Line 5, which provides half of the oil supply for Ontario and Quebec). Michigan’s lawyers countered that the pipeline violates the state’s ability to manage its natural resources, making this a matter for state court.

With the question of jurisdiction answered, legal experts said state courts can now decide whether the portion of the pipeline spanning the Straits should be shut down. A unanimous decision by the high court is a “big deal,” said Andy Buschbaum, lawyer for the Great Lakes Business Network, which filed briefs in support of the attorney general.

“The justices of the court, regardless of ideology, agreed that it’s the state court that’s the proper court to hear this dispute,” he said. “We’re finally in a position for the state court to actually decide whether Line 5 belongs on the bottom of the Great Lakes, or whether there are alternatives.” 

Arguing the case in Michigan’s 30th Circuit Court also is expected to sharpen the focus on tribal sovereignty. All 12 federally recognized tribes in the state have called for Line 5 to be shut down, saying it threatens their waters, treaty rights and ways of life. They were not part of the Supreme Court proceedings. 

“It will really create space now for tribes to uplift their voices in the proceedings, to uplift tribal treaty rights, to uplift the protection of natural resources and ultimately the preservation of our cultural lifeways,” said Whitney Gravelle, president of the Bay Mills Indian Community, one of the parties involved in separate litigation against Line 5.

The case won’t be heard until an appeal of a separate case moves through federal court. Enbridge sued Michigan Governor Gretchen Whitmer for trying to shut down Line 5 in 2021, arguing that the state has no authority over pipeline safety. The Sixth Circuit Court of Appeals sided with the company in November, and Whitmer appealed the decision in January.

Asked about the Supreme Court decision, Enbridge spokesperson Ryan Duffy cited the Sixth Circuit ruling that said the federal government regulates Line 5’s safety. The Pipeline and Hazardous Materials Safety Administration has found “no safety issues that would warrant its shutdown,” Duffy said.

The legal back and forth comes amid ongoing court and regulatory battles over Enbridge’s plan to replace the aging dual pipelines beneath the Straits with a tunnel housing a segment buried beneath the lakebed. 

The company is awaiting various state and federal permits, with decisions expected this summer. And last month, the Michigan Supreme Court heard oral arguments from tribes and environmental groups trying to overturn a permit the Michigan Public Service Commission issued in 2023.

Lawyers for Enbridge defended the proposed tunnel last month, claiming it would make a safe pipeline even safer. “Under any standard, this safety and environmental upgrade is more protective of the environment than the status quo or any alternative,” said John J. Bursch, a lawyer for Enbridge.

And in Wisconsin last week, a state court heard arguments in the Bad River Band of Lake Superior Chippewa’s bid to stop construction on a segment of Line 5 that crosses the tribe’s watershed. Gravelle said the Bay Mills Indian Community is supporting the Wisconsin tribe’s litigation against the pipeline.

“Line 5 is such a complicated issue. But those are not just legal questions. They’re also moral ones and they ultimately ask us what kind of future we choose to protect,” Gravelle said.

This story was originally published by Grist with the headline Michigan wins key legal battle over Line 5 pipeline on Apr 27, 2026.