PORTLAND, Maine (AP) — Maine election officials on Monday certified that opponents of a $1 billion electricity transmission corridor have enough valid signatures to move forward with a referendum.

More than 80,000 signatures were certified, exceeding the threshold of 63,067 signatures for the ballot, Secretary of State Shenna Bellows said.

The Maine Legislature will now consider this initiative. If lawmakers reject it, then there would be a vote in November.

But Jon Breed, who heads up the Clean Energy Matters campaign, said his group intends to conduct its own review of the signatures.

“Fossil fuel companies spent more than a million dollars on paid signature gathering efforts,” he said, adding that the financial incentives in exchange for signatures “warrants our utmost scrutiny.”

The referendum would require legislative approval for any electrical power line project that exceeds 50 miles (80 kilometers) and would impose a prohibition on such a project in the Upper Kennebec Valley. It also would be retroactive to September 2014.

Much of the New England Clean Energy Connect calls for widening existing corridors, but a new swath would be cut through 53 miles (85 kilometers) of woods in western Maine.

It’s the second referendum attempt aimed at stopping the project, which would bring 1,200 megawatts of hydropower to the New England grid.

Opponents previously collected more than 63,000 signatures for a “People’s Veto” referendum that was deemed unconstitutional by the Maine Supreme Judicial Court. The state Supreme Court ruled that such a referendum can be used to nullify legislative actions but not state agency decisions.

Sandi Howard, a leading opponent of the project, called news of the referendum’s certification “bittersweet.”

“It’s bitter because the people of Maine should have had their say last November, but it’s sweet because it shows that no matter what CMP or their high powered lawyers throw at us, opposition to the project remains as strong as ever,” she said.

The new referendum could be open to legal challenges, as well.

Orlando Delogu, professor emeritus at the University of Maine School of Law, contends the referendum is unconstitutional because it targets a single company, violates separation of powers, and illegally changes a law retroactively to alter the consequences.