Supreme Court Rules For Public Interest in Line 5 Case

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In a ruling that puts vital decisions about operating the Line 5 oil pipeline back in a Michigan state court, the U.S. Supreme Court unanimously decided on April 22 against the effort by Enbridge Inc., the Line 5 owner, to move the case to federal court. 

The high court’s ruling came in response to a procedural issue. Enbridge asked for the change in venue for considering a lawsuit filed by Michigan Attorney General Dana Nessel 857 days after a mandatory 30-day deadline to do so.  

The Sixth Circuit Court of Appeals had already held that Enbridge’s removal of the lawsuit to federal court was untimely and unjustified. Enbridge appealed that decision to the US Supreme Court, which heard oral arguments in the case (Enbridge Energy, LP v. Nessel) on February 24.

Michigan Attorney General Dana Nessel filed the state lawsuit in June 2019 to void the 1953 easement allowing Line 5 to operate beneath the Straits of Mackinac. Now the case returns to Michigan state court, where arguments will be heard whether to enforce a shutdown of the pipeline, which transports oil between Wisconsin and Ontario.

In the Supreme Court opinion authored by Justice Sonia Sotomayor for the court, Sotomayor wrote that “Enbridge’s counterarguments are not persuasive.”

Opponents of Line 5, led by Nessel, and aided by state and regional environmental groups, say the U.S. Supreme Court ruling is essential to confirming core legal principles that states have sovereignty over their waters, and have primacy over federal law in managing Great Lakes waters and land.

Circle of Blue has closely followed the state’s effort to shut down the 645-mile long pipeline, including in this December 2025 article summarizing the various court battles.

Enbridge, joined by the Trump administration, argues the opposite. The federal Pipeline Safety Act, initially enacted in 1968, gives the Pipeline and Hazardous Materials Safety Administration (PHMSA), a unit of the Department of Transportation, exclusive authority to regulate Line 5. Enbridge also cites the Transit Pipelines Treaty, signed by Canada and the U.S. in 1977, that blocks any measures that would impede, divert, or interfere with the transit of oil and gas through pipelines in either country.

In December 2025 Judge Robert Jonker of the Western District of Michigan ruled in favor of Enbridge on both those arguments.

Lead image: Enbridge, Inc.’s Line 5 pipeline splits in two and crosses beneath the waters of the Straits of Mackinac, near the site of Michigan’s Mackinac Bridge. Photo © J. Carl Ganter / Circle of Blue