The Maine Public Utilities Commission’s approval of a proposed 145-mile transmission line that would bring Canadian hydropower to the New England power grid was “replete with errors,” according to a company that’s suing to stop the project.

In an appeal of that approval to the Maine Supreme Judicial Court, NextEra Energy Resources accused the commission of ignoring state law requiring a third-party review of alternatives to Central Maine Power’s transmission line. NextEra also said the panel failed to follow the law in determining a public need for the $1 billion project.

“Accordingly the commission’s order is replete with errors as a matter of law that contravene explicit mandates and the intent of the Maine Legislature,” lawyers for the company wrote.

The three-member commission concluded that a third-party analysis was unnecessary because there was no feasible substitute for providing 1,200 megawatts of renewable energy.

The litigation is playing out as Maine’s Department of Environmental Protection and Land Use Planning Commission prepare to issue their own decisions on the project. Opponents, meanwhile, are considering pushing to put the $1 billion project to a statewide vote.

The appeal brought by NextEra Energy, which owns the oil-fired Wyman Power Station in Yarmouth, won’t be settled before the final votes are made by regulators. Central Maine Power has until the fall to issue a response to NextaEra’s arguments, which were filed Monday.

The New England Clean Energy Connect would allow Canadian hydropower to reach consumers in Massachusetts to meet that state’s green energy goals.

Much of the project calls for widening existing corridors, but a new swath would be cut through 53 miles of wilderness in western Maine. The new corridor would cross the Appalachian Trail, wetlands and streams on land that’s already owned by CMP.

Critics said Maine forests shouldn’t be spoiled for a project that would benefit residents in Massachusetts. They also say it would snuff out homegrown solar and wind projects in Maine.

But Maine’s public advocate and others say the project will lower electricity rates for everyone in the region while the construction cost would be borne by ratepayers in Massachusetts.

Supporters say the project would provide electricity for 1 million homes, drive down electricity rates and reduce carbon pollution.

Central Maine Power on Tuesday called the project “the singular most important and comprehensive project to combat climate change in Maine and New England.”

The utility is also providing $258 million in incentives that would provide $140 million for rate relief for retail customers, $50 million for low-income energy customers, $15 million to subsidize heat pump purchases, and $15 million for electric cars and charging stations.

A subsidiary of CMP, which is part of Connecticut-based Avangrid, would be created to oversee construction of the power line to ensure Maine ratepayers are insulated from costs.

This story was corrected at 8 p.m. on Aug. 7, 2019. The Associated Press reported erroneously the type of fuel used by the Wyman Power Station in Yarmouth. The plant is fueled by oil.