THE MAINE SUPREME Judicial Court on Tuesday breathed new life into a Massachusetts-financed power line designed to carry hydroelectricity from Canada to Lewiston and from there into the New England power grid.

Fifty-nine percent of Maine voters passed a law in November that retroactively blocked the transmission line from being built through the heavily wooded Upper Kennebec region of Maine, but the court held that key sections of the law were unconstitutional because they deprived the company building the line of rights that had already vested.

The project, known as New England Clean Energy Connect, still faces some hurdles, but the decision appears to pave the way for the transmission line to resume construction. The power line, capable of carrying a large, steady amount of hydroelectricity on an around-the-clock basis, is a key part of Massachusetts’ game plan to reduce reliance on fossil fuels and push back against climate change.

The unanimous decision hinged on whether the voters of Maine had the authority to retroactively shut down a project that had moved forward after receiving a Certificate of Public Convenience and Necessity from the state’s Public Utilities Commission.

The certificate, whose legality was subsequently upheld by the high court in Maine, was issued on May 3, 2019. Construction on the transmission line began on January 18, 2021. By November 3, 2021, according to the court’s decision, New England Clean Energy Connect had spent $450 million on the project, 43 percent of the entire budget.

“We hold that NECEC could reasonably rely on the Certificate of Public Convenience and Necessity, and our judgment affirming the [certificate], as valid authorization to begin construction such that its right to proceed according to the [certificate’s] terms could vest upon evidence that it undertook significant, visible construction in good faith, according to a schedule that was not created or expedited for the purpose of generating a vested rights claim,” the court held.

“Good faith” is crucial, since some have argued that New England Clean Energy Connect recklessly pushed forward with the project in January 2021 even though it was well aware a ballot petition was in the works seeking to derail the project.

“We do not accept the argument’s implicit premise that, to be acting in good faith, a developer must wait to commence construction pursuant to a valid permit if there is a possibility that a retroactive change in the law could affect the right to complete a project,” the court held. “As of January 2021, all that existed was a petition in circulation. There was no indication whether sufficient signatures had been gathered for the ballot measure to be presented to the Secretary of State, whether the Secretary of State would certify that the petition had garnered enough valid signatures to be presented to the Legislature, or whether the Legislature (or Maine voters acting in its stead) would approve the then-hypothetical initiative.”

Nevertheless, the court remanded to a lower court a decision on whether New England Clean Energy Connect had acted in good faith. The court also noted that its decision would have no impact on a number of other approvals needed to complete the project.

The company behind New England Clean Energy Connect is Avangrid, the same company behind two of the wind farms approved by the state of Massachusetts. The supplier of the electricity would be Hydro-Quebec, the provincial company seeking to expand its market into New England.

Opposition to New England Clean Energy Connect was fanned by companies, including NextEra Energy, that perceived approval of the power line as a threat to their existing power-generating businesses.

Troy Wall, a Baker administration spokesperson, issued a statement calling the project “a key component of the Commonwealth’s net zero emissions strategy. …  The ruling from the Maine Supreme Judicial Court on the transmission line project is encouraging, and the administration will continue to closely monitor the legal processes.”