A dump truck loaded with wood debris navigates a steep hill along the NECEC corridor in Johnson Mountain Township in November 2021. Gregory Rec/Staff Photographer

Avangrid Inc., the parent company of Central Maine Power Co., has sued NextEra Energy in federal court, accusing the energy giant of causing more than $350 million in business damage as it tried to sabotage the New England Clean Energy Connect transmission line project.

It’s the latest round in a yearslong legal dispute over the $1.5 billion line in western Maine intended to bring hydropower from Canada to the New England electric grid.

Avangrid, the Connecticut-based developer of the 145-mile transmission line, says in the lawsuit it filed Tuesday in U.S. District Court in Springfield, Massachusetts, that NextEra has engaged in “anticompetitive, unfair and deceptive business practices to foreclose competition for the supply of wholesale electricity.”

NextEra has “reaped hundreds of millions of dollars from these illegal practices,” Avangrid said.

It accused NextEra of looking to “sabotage” Massachusetts’ clean energy transition through “sham litigation, sham and defective referenda, the use of dark money in violation of applicable campaign finance law, and the use and dissemination of false and misleading statements.” NextEra delayed the transmission line with “baseless challenges to and appeals” of permits that were ultimately approved, Avangrid said.

Avangrid is seeking unspecified monetary damages and an injunction against NextEra to prevent it from “continuing to undertake its anticompetitive scheme.”

Chris McGrath, a spokesman for NextEra, said the company just received a copy of the lawsuit and is reviewing it. “We look forward to vigorously defending against these claims in court,” he said.

Massachusetts ratepayers are a beneficiary of the power corridor. Three Massachusetts utilities and Avangrid agreed recently that Massachusetts ratepayers will shoulder $512 million in additional costs caused by delays in the construction of the project.

The U.S. Court of Appeals for the District of Columbia Circuit last month upheld a decision by the Federal Energy Regulatory Commission directing NextEra to install a circuit breaker at Seabrook. Avangrid accused NextEra of failing to perform a necessary safety upgrade of equipment at the plant, blocking the NECEC project.

The Maine Ethics Commission said last year that NextEra Energy concealed its identity as a large donor to Democrats shortly before the 2018 election and funded a group that should have registered as a political action committee the following year when it worked to oppose the transmission line that was rejected in 2021 by voters. In court battles that followed, NECEC’s backers said the project had established “vested rights” to continue construction and a Cumberland County jury decided in 2023 that the project could resume.

Avangrid accuses NextEra of spending $20 million of a total of $24 million to pass the 2021 ballot measure that would have halted the project. But Avangrid also spent heavily during that campaign to defeat the ballot question. About $63 million was spent to oppose it, led by political action committees tied to Avangrid and Hydro-Quebec, according to the Maine Ethics Commission.

Avangrid reported to the Maine Public Utilities Commission last summer that it’s making progress on construction after resuming work in October 2023. Access to the route was about 80% complete at the time of the July 1 report, it said.

Avangrid says in its lawsuit that NextEra “abused the regulatory and judicial process, misled voters with illegal dark money and false statements, and obstructed electric infrastructure improvements.” It did so to “line its own pockets by excluding lower-priced competition for electricity supply,” it said.

It accused NextEra of mounting at least 10 “baseless and failed challenges” to permitting and approval, “delaying NECEC by years.” NextEra challenged three licensing procedures before regulatory agencies and lost each time, Avangrid said. NextEra unsuccessfully appealed the three decisions, Avangrid said.

“In its scorched-earth campaign, NextEra did not stop at sham regulatory challenges and sham litigation,” Avangrid said. “NextEra created and supported two failed unconstitutional referenda that were directly aimed at delaying NECEC.”