The US Supreme Court this week has agreed to hear whether a lawsuit over Enbridge’s Line 5 pipeline belongs in federal or state court. This marks the latest development in a long-running dispute between Enbridge and the State of Michigan, which centres on an underwater section of Line 5 in the Straits of Mackinac.

The 540,000 barrel per day (bpd) pipeline carries oil and natural gas liquids (NGLs) for use in Michigan and also into Canada.

The Supreme Court has taken up Enbridge’s appeal of a lower court's ruling last year rejecting the company's request to move the case from state court to federal court. The 6th US Circuit Court of Appeals ruled that Enbridge had taken too long to seek the transfer of a 2019 lawsuit by Michigan Attorney General Dana Nessel to federal court, which it attempted to do in 2021. That ruling marked the reversal of a separate 2022 decision that the case should be heard in federal court.

Enbridge’s attempts to move the case to federal court are in line with expectations that federal courts are likely to be friendlier to defendants in such cases. In its appeal to the Supreme Court, the company cited conflicts between decisions from lower courts. Specifically, it pointed to a split within the regional US appeals courts over whether the judiciary can allow exceptions to the time limit for seeking to move cases filed in state court to federal court.

The Supreme Court did not explain its rationale for taking up the matter. It will now weigh the question of what court the case belongs in during its next term, which is scheduled to begin in October. Enbridge officials were cited by the Associated Press as saying the company was encouraged by the Supreme Court’s move.

Nessel’s lawsuit seeks to void the easement that allows Enbridge to operate the 4.5-mile (6.4-km) section of Line 5 that runs under the Straits of Mackinac. Meanwhile, the US Army Corps of Engineers last month said it expects to make a decision in the autumn on whether to grant Enbridge a permit to build a tunnel to house underwater pipeline section. The regulatory approval process is moving forward regardless of how the court case plays out.