The 6-1 decision found that a state commission did not examine the full scope of possible harm to the environment. Environmental groups and tribal nations appealed the decision, landing the case before the state’s highest court this year. By broadening the scope of reviews under the Michigan Environmental Protection Act, opponents said conversations about shutting down the entire pipeline are finally a possibility. Separate from the tunnel project, Line 5 faces legal challenges from groups that have fought to shut down the pipeline for years, including Governor Gretchen Whitmer’s administration. This spring, a unanimous ruling from the U.S. Supreme Court paved the way for state court proceedings on whether the aging pipeline can continue operating in the straits.