U.S. Supreme Court Rejects Michigan's Appeal in Line 5 Pipeline Dispute

Supreme Court Denies Michigan's Sovereign Immunity Claim Against Enbridge

The U.S. Supreme Court has rejected Michigan's appeal in a high-profile legal dispute over the controversial Line 5 oil pipeline, leaving in place lower court rulings that allow Enbridge Energy to maintain operations of the infrastructure running through the Straits of Mackinac.

The decision means that Michigan Attorney General Dana Nessel's office and Governor Gretchen Whitmer's administration will not be able to pursue their sovereign immunity argument in federal court, effectively ending that particular legal avenue in the years-long battle over the pipeline.

What the Decision Means

The Supreme Court denied Michigan's petition for a writ of certiorari on Tuesday, March 31, leaving standing a lower court ruling that Enbridge's lawsuit against the state falls within an exception to sovereign immunity. That exception applies when litigation alleges a violation of federal law or the U.S. Constitution.

According to the Sixth Circuit Court of Appeals panel that decided the case last year, Enbridge's suit does not seek to extinguish the state's regulatory authority over the submerged lands entirely. Instead, the company is asking that Michigan's regulatory activities be brought into compliance with federal pipeline safety laws and constitutional requirements.

"We are disappointed by the Supreme Court's decision not to review this important issue of state sovereignty," said Danny Wimmer, press secretary for Attorney General Dana Nessel's office. "We will continue to fight for the people of Michigan on these vital issues concerning the Line 5 pipelines in the Straits."

Enbridge spokesperson Ryan Duffy said the company agreed with the lower court's interpretation. "The Sixth Circuit made clear that Enbridge's suit falls within the exception to sovereign immunity," Duffy said.

The Background

The conflict over Line 5 has been ongoing since 2019, when Governor Whitmer's administration began pursuing legal challenges to Enbridge's operations. The pipeline, operated by Canadian company Enbridge, carries crude oil and natural gas liquids from western Canada through Wisconsin and Michigan, including a controversial stretch beneath the Straits of Mackinac.

Along that section, Line 5 consists of two 20-inch parallel pipelines that run along the lakebed between Lake Michigan and Lake Huron. The infrastructure transports as much as 23 million gallons of crude oil and natural gas liquids each day, supplying 10 refineries and propane production facilities across both the United States and Canada.

In 2020, Governor Whitmer revoked Enbridge's 1953 easement that allowed the operation of the twin underwater pipelines on the bottom of the Lake Michigan side of the Straits. That action prompted Enbridge to file suit in federal court seeking an order to keep the pipeline running.

The U.S. District Court ruled in December that federal law governing pipeline safety preempts the state's multi-year effort to shutter the line. Nessel's office then filed the petition with the U.S. Supreme Court in November, seeking a final ruling on the sovereign immunity question.

A Tunnel Alternative

While Michigan pursues legal challenges, Enbridge has been working on an alternative solution. The company has proposed building a tunnel beneath the lakebed to house a replacement segment of the pipeline, arguing it would significantly reduce the risk of a catastrophic spill.

The proposed tunnel would be roughly four miles long, running under the Straits of Mackinac not far from the Mackinac Bridge. Enbridge says the tunnel would make the pipeline even safer, though environmental groups continue to push for a complete shutdown.

"We are continuing to evaluate the application that was submitted," said Scott Dean, spokesperson for the Michigan Department of Environment, Great Lakes and Energy (EGLE), which is reviewing Enbridge's permit application. "We will include this document, along with many others posted to the EGLE database, as part of our review."

A decision from EGLE on the permit is expected no later than mid-July. The Michigan Public Service Commission has already issued a permit for the project, but an appeal of that permit sits before the Michigan Supreme Court.

Other Legal Fights Continue

Despite this setback at the federal level, two major legal fights over Line 5 remain active.

In Michigan state courts, opponents of the pipeline — including Native American tribes and environmental groups — have challenged the permit Enbridge needs to build the tunnel. They argue that the Michigan Public Service Commission rushed or limited its review by not fully considering environmental risks, alternatives, and the broader need for the pipeline. They're asking the Michigan Supreme Court to send the permit back for a more thorough review, while Enbridge and supporters argue the tunnel is the safest option.

Arguments before the state's highest court were heard in March of 2026, with a ruling pending.

Separately, a federal lawsuit filed by the Bad River Band of Lake Superior Chippewa in Wisconsin could ultimately determine whether Line 5 must be rerouted or shut down in parts of the Upper Midwest. The tribe is seeking to force a shutdown or reroute of the pipeline, arguing it operates illegally on tribal land. The tribe has also invoked a 1977 treaty that prevents either country from taking actions in relation to a pipeline that may harm the energy supply in either country. Those negotiations are ongoing.

Campaign Promises and Reality

For Governor Whitmer and her Democratic colleagues in Michigan, this latest setback at the Supreme Court serves as another reminder that courtroom victories don't always flow as easily as campaign promises. The administration campaigned on promises to shutter the more than 70-year-old pipeline, initiating litigation between 2019 and 2020 after negotiations to speed up the construction of a tunnel to house the line failed.

In late 2018, then-Governor Rick Snyder entered into an agreement with Enbridge, in which the company promised to build a tunnel under the Straits of Mackinac to house a new segment of Line 5 and protect it from potential anchor strikes or other disturbances. Enbridge has secured most of its state permits for the tunnel, but is still waiting for the completion of a federal review before it can begin construction.

The Supreme Court's decision on sovereign immunity doesn't resolve the substantive issues surrounding the pipeline's safety or necessity. It simply forecloses one legal argument that the state had pursued. Environmental groups argue that an oil spill in the Straits would be devastating across the Great Lakes, while Enbridge maintains that the pipeline is operating in accordance with federal law and interstate commerce regulations.

The company says the tunnel will make Line 5 an even safer means of transporting crude oil and natural gas liquids through the region. "Line 5 is operating in accordance with federal law, interstate commerce regulations, and international treaty obligations," Duffy said. "These frameworks recognize the essential role Line 5 plays in meeting the energy needs of the Great Lakes region and supporting its economic vitality."

As the legal battle continues on multiple fronts, the future of Line 5 remains uncertain. The Supreme Court's refusal to take up Michigan's appeal doesn't end the dispute — it simply shifts the focus to other legal challenges that will determine whether the pipeline can continue operating as planned.