Supreme Court Rejects Michigan's Line 5 Sovereignty Claim, Opens Federal Door for Enbridge Lawsuit

U.S. Supreme Court Denies Michigan's Appeal in Line 5 Pipeline Case

LANSING — The U.S. Supreme Court has rejected Michigan's appeal arguing that the state has sovereign immunity from an ongoing lawsuit by Enbridge Energy regarding its controversial Line 5 pipeline in the Straits of Mackinac.

The decision means Enbridge can proceed with its federal lawsuit to maintain operations of the pipeline, a move that has drawn sharp criticism from Governor Gretchen Whitmer and Attorney General Dana Nessel, who have spent years trying to shut down the decades-old facility.

What the Decision Means

On March 30, the Supreme Court declined to take up Michigan's appeal, leaving in place a lower court ruling that allows Enbridge's case to proceed in federal court rather than state court. The state lost in the U.S. Court of Appeals for the Sixth Circuit, which ruled that Enbridge's suit falls within an exception to sovereign immunity.

"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. "We will continue to fight for the people of Michigan on these vital issues concerning the Line 5 pipelines in the Straits."

Enbridge spokesman Ryan Duffy responded, "The Sixth Circuit made clear that Enbridge's suit falls within the exception to sovereign immunity."

The Line 5 Dispute

The Line 5 pipeline is a decades-old Enbridge facility that carries crude oil and natural gas liquids from western Canada through Wisconsin and Michigan, including a controversial stretch beneath the Straits of Mackinac. In that section, Line 5 consists of two 20-inch parallel pipelines that run along the lakebed.

Line 5 transports as much as 23 million gallons of crude oil and natural gas liquids each day. Along the way, it supplies 10 refineries and propane production facilities across both the United States and Canada.

Governor Whitmer and Attorney General Nessel have continued to push for a shutdown instead, citing environmental risks to the Great Lakes. Critics of that effort say the pipeline remains vital to regional energy supplies.

Enbridge's Tunnel Proposal

Enbridge has proposed building a tunnel deep below the lakebed to house a replacement segment of the pipeline, arguing it would significantly reduce the risk of a spill. 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 in an email to Michigan Public Radio. "These frameworks recognize the essential role Line 5 plays in meeting the energy needs of the Great Lakes region and supporting its economic vitality."

State's Shutdown Push

The shutdown push vs. energy reality has been a defining issue for Whitmer's administration. Democratic leaders in Michigan, including Governor Whitmer and her AG Dana Nessel, have continued to push for a shutdown instead, citing environmental risks to the Great Lakes.

Critics of that effort say the pipeline remains vital to regional energy supplies and that the tunnel project offers a long-term solution to replace the aging dual pipelines beneath the Straits of Mackinac while maintaining a steady and secure energy supply.

Litigation History

Litigation over the Line 5 project has been ongoing since 2019, including Governor Whitmer's administration appealing to the Supreme Court in 2025, arguing that the state has "sovereign immunity" from Enbridge's lawsuit to maintain operations of the pipeline.

Attorneys for the Whitmer administration had argued that the state, whose highest court holds a Democratic majority, should control disputes over "state-owned submerged bottomlands." But the federal courts, and now the Supreme Court by staying silent, didn't buy the argument.

Not Game Over

Despite the loss, this legal saga is far from finished. Two major fights over Line 5 are still bubbling:

Michigan Supreme Court: This case is about whether Michigan regulators properly approved Enbridge's plan to build a tunnel beneath the Straits of Mackinac to house the aging Line 5 pipeline. Opponents – including Native American tribes and environmental groups – argue 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 to prevent a potential oil spill and keep energy flowing. Arguments were heard in March of 2026 and a ruling is pending.

Federal lawsuit in Wisconsin: A separate case could ultimately determine whether Line 5 must be rerouted or shut down in parts of the Upper Midwest. It focuses on whether Enbridge is illegally operating the Line 5 pipeline across tribal land belonging to the Bad River Band of Lake Superior Chippewa. The tribe is seeking to force a shutdown or reroute of the pipeline off its reservation.

Campaign Reality Check

For Governor Whitmer and her anti-Enbridge Democratic colleagues, this latest setback at the Supreme Court is another reminder that courtroom wins don't always flow as easily as campaign promises. The administration is still fighting – but for now, the Supreme Court has made one thing clear: at least one of Whitmer's pipeline fights isn't staying on Michigan's home turf.

The decision represents a significant legal setback for the Whitmer administration's efforts to shut down Line 5, but the broader debate over the pipeline's future continues in both state and federal courts.