The Michigan Supreme Court on Friday ruled that the Michigan Public Service Commission erred when it granted a key permit for the Line 5 petroleum pipeline tunnel under the Straits of Mackinac. The issue reached the state Supreme Court after the Michigan Court of Appeals sided with the state. The justices also found that, when analyzing possible alternatives to the tunnel project — a required step in the permitting process — commissioners applied their analysis inconsistently. “I think this is the most important opinion from the Michigan Supreme Court under (the Michigan Environmental Protection Act) in probably decades,” Scott said. The other is on hold in state court pending the outcome of the first case.