PORTLAND — Maine residents overwhelmingly voted to halt a $1 billion electric line that is already under construction, but that doesn’t spell the end of the polarizing project in the state's western woods.

Workers reported for duty constructing the power line as usual Wednesday, and project supporters filed a lawsuit challenging the referendum’s constitutionality.

“It’s not the end of the road. We’re going to continue to advocate for the project,” Thorn Dickinson, president and CEO of the New England Clean Energy Connect, said Wednesday.

Pete Didisheim from the Natural Resource Council of Maine, which opposed the project, gave the lawsuit little chance of success and said Mainers are going to be “furious” over continuing construction.

He urged Central Maine Power, the Maine Department of Environmental Protection and the state of Massachusetts “to honor the will of Maine voters and stop this project.”

The 145-mile (233-kilometer) power transmission line would serve as a conduit for up to 1,200 megawatts of Canadian hydropower and would be fully funded by ratepayers in Massachusetts. Most of it would be built along existing corridors but a new 53-mile (85-kilometer) section is being cut through the woods to reach the Canadian border.

Supporters contend the renewable energy — enough to power 1 million homes — will remove carbon from the atmosphere and stabilize energy prices, benefiting the entire region.

Critics say the environmental benefits are overstated and that the project would forever change the character of the forest.

The latest legal challenge, filed Wednesday by CMP’s corporate parent, Avangrid, contends the referendum violates separation of powers, a principle regarding retroactive laws, and a provision protecting contracts.

It seeks an injunction to prevent enforcement of the referendum to ensure construction can proceed while the lawsuit is heard.

Orlando Delogu, professor emeritus at the University of Maine Law School, said “ex post facto” laws, which retroactively target something that was previously legal, violate the Maine Constitution.

“I like Avangrid’s chance of prevailing in the final analysis,” said Delogu, who supports the project.

Sandi Howard, a leading critic of the project, said the lawsuit and construction “exemplifies the arrogance” that the Central Maine Power has shown toward Maine ratepayers.

Mainers don’t want “this kind of commercial exploitation and large-scale industrial development in western Maine,” she said.

Jake O’Neill from the Conservation Law Foundation, which supports the project, said clean energy sources like hydropower represent “the only path forward in dealing with the climate crisis.”

“As this fight likely winds its way through the courts, polluting fossil fuels are still powering much of New England’s grid and polluting our communities and planet in the process,” he said.

In Maine, voters signaled their disapproval of the project Tuesday with about 59% voting to spike the project. The law would go into effect 30 days after the secretary of state and governor sign off, putting the date in early January, Didisheim said.

The referendum and lawsuit aren’t the only factors at play when it comes to whether the project moves forward.

Parties are awaiting a Maine Supreme Court decision on 1-mile portion of state land that is part of the project, and the Maine Department of Environmental Protection is deciding whether to revoke the project’s permit.

Maine Democratic Gov. Janet Mills, who supported the project, said the project’s failure to proceed would be a lost opportunity “to advance the clean energy goals that are vital to combating climate change."

In Massachusetts, which selected the project to meet its clean energy goals, the administration of Republican Gov. Charlie Baker will be working with Avangrid and regional partners on the path “to securing more affordable, renewable energy for Massachusetts,” said Craig Gilvarg, communications director for the state’s office of Energy and Environmental Affairs.