A state judge has vacated a lease of public land to Central Maine Power Co. for a 1-mile section of a planned 145-mile transmission corridor through western Maine, jeopardizing the entire project.

Superior Court Justice Michaela Murphy said in her ruling Tuesday that state public land officials failed to make a required finding that the lease would result in no reduction or substantial alteration to the public lands being leased and, therefore, the agreement was not valid.

Thorn Dickinson, head of the company that will build the corridor, NECEC Transmission, issued a terse statement saying the company is “reviewing the Superior Court’s decision to determine our next steps on the matter.” Opponents, meanwhile, said the ruling will, at the least, create a substantial hurdle for the company’s plan.

CMP holds the lease for the land in question, but is transferring it to NECEC Transmission, the company that was formed to oversee construction of the project. Both CMP and NECEC Transmission are owned by Avangrid, the U.S. subsidiary of Iberdrola Group, a multinational energy company based in Spain.

Environmental groups that oppose the project sued, objecting to the state’s lease to CMP of a 33-acre tract of publicly owned land in West Forks and Johnson Mountain that is roughly 1 mile long and 300 feet wide. The original lease was signed in 2014 under the Paul LePage administration and a new lease was signed last year under Gov. Janet Mills.

The original lease called for rent of $1,400 a year. That was increased under the new lease to $65,000, along with a provision that allowed CMP to transfer the lease to NECEC Transmission.

In neither case did the Bureau of Public Lands inform the public or the Legislature of the planned leases ahead of time, Murphy’s ruling said, and there’s no evidence that the Bureau of Public Lands met a requirement to determine that the public land would not be reduced or its use substantially altered by the lease. She said that the bureau also skirted a requirement that the deal go to the Legislature and be approved by a two-thirds vote of both houses.

The decision means corridor-builder NECEC Transmission will have to go back to the state to negotiate the lease of the public land that will be used for part of the corridor, which would connect hydroelectric power generated in Quebec with the New England power grid in Lewiston. Most of the electricity being generated is intended for Massachusetts power customers, who are paying for the project.

Backers said the project will generate 1,600 jobs and boost the Maine economy. Construction began this year and NECEC Transmission has said it expects the corridor to be complete by mid-2023. It’s unclear how Murphy’s ruling might affect that timetable.

The corridor project has been controversial, and a referendum question on the ballot in November will ask voters if they want to have all leases of public lands put before the Legislature, requiring a two-thirds vote for approval. The measure would be retroactive, meaning the Legislature would have to review and vote on any public land leases for the NECEC corridor project, which has received approval from regulatory bodies, but has spawned opposition among many in the state, including some legislators.

Though Murphy’s ruling said the one thing both sides would likely agree on is that her decision is likely to be the subject of appeals, critics of the project still hailed her decision.

“Now, (Avangrid) will have no choice but to negotiate the terms of the public lease in an open and transparent way,” Tom Saviello, the lead signer of the petition that put the referendum on the November ballot, said in a statement.

“With this ruling, the entire CMP corridor is rightfully at risk,” Darryl Wood, a volunteer with the group No CMP Corridor, said in a statement. “CMP no longer has title right and interest for the full route, so if they continue to build it, it will be a power line to nowhere.”