Federal ruling protects Line 5 pipeline in Straits of Mackinac

A federal judge thwarted a long-running attempt by the state of Michigan to stop Enbridge from operating the segment of Line 5 running under the Straits of Mackinac. Line 5 is a light crude oil and natural gas liquids pipeline.

Citing safety and environmental concerns, state officials had moved in November 2020 to prevent Enbridge, which owns and operates the 645-mile-long pipeline, from using a 4-mile strip of Line 5 under the straits, effectively closing the line entirely. In 1953, the state granted Enbridge’s predecessor an easement that allowed it to construct two 20-in. diameter pipelines under the Straits of Mackinac, which connects Lake Michigan and Lake Huron.

Enbridge argued that federal law preempts such a move by state officials, and U.S. District Judge Robert J. Jonker agreed with the company. According to his opinion and order, Congress expressly preempted state regulation of interstate pipeline safety through the Pipeline Safety Act of 1992.

“Pipeline safety generally, and protection of the Straits of Mackinac, are critical interests to be sure. But when it comes to Line 5, they are the responsibility of the United States, and Michigan lacks the power to interfere,” the judge wrote in his December 2025 decision.

Line 5 transports up to 540,000 barrels (22.48 million gallons) of light crude, synthetic crude and natural gas liquids, which are refined into propane. It transports more than half of Michigan’s statewide propane needs and about 65 percent in the Upper Peninsula.

Enbridge, based in Canada with offices in the United States, has been planning to replace the dual pipelines with a single pipeline in a tunnel deep below the lakebed, pending the necessary approvals.

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