The Maine Department of Environmental Protection has suspended the construction license for the New England Clean Energy Connect project, the latest step in a battle that has been fought in the courts and at the ballot box.

In a ruling issued Tuesday, DEP Commissioner Melanie Loyzim said all construction work is to stop until the project’s developer either wins its legal fight over a public land lease in the project’s path or its constitutional challenge to the recently passed referendum question or if a court issues an injunction allowing work to continue while the legal maneuvering takes place.

Loyzim’s ruling settles, at least temporarily, a controversy over NECEC’s decision to continue work on the $1 billion transmission corridor after roughly 60 percent of Maine voters approved a referendum question designed to block the corridor. NECEC officials filed a suit challenging the constitutionality of the referendum the day after the election and said it would continue construction work while that challenge was pending.

But critics cried foul and said the move was a direct challenge to the will of the voters. NECEC eventually said last week that it would suspend construction voluntarily after a request by Gov. Janet Mills.

The DEP has been under mounting pressure for months from project opponents to suspend the license it issued for the project and shut down construction while the legal and regulatory challenges play out.

The agency held a hearing Monday to weigh whether to suspend NECEC’s permit to build the transmission corridor that is designed to carry electricity generated by hydroelectric generators in Canada to a New England transmission grid hub in Lewiston and ultimately to electric customers in Massachusetts, who are footing the bill for the project.

At the hearing, opponents of the project said that the pending law adopted by voters should be assumed to be constitutional unless and until a court decides otherwise. But the developer noted that the law won’t legally take effect until Dec. 19 and the voluntary suspension meant the DEP wouldn’t need to act until the court rules on NECEC’s request for a preliminary injunction to keep the law from going into force.

But Loyzim’s ruling suggests that there was no almost no way for her to not suspend the license to build the project.

“To not suspend the license would allow: continued construction in the region where such construction will shortly be banned; continued construction of other Project segments without a reasonable expectation that those segments will ever be part of an alternative route and energized to fulfill the original purpose of the Project; and construction of a type of project that shortly will not be authorized for lack of having received 2/3 approval of both houses of the Legislature,” she wrote.

Loyzim also said that the voluntary suspension isn’t legally binding or enforceable by the DEP and so her department couldn’t depend on it stopping work.

“So long as the License is suspended, all construction must stop,” she said, although her order allows NECEC to “stabilize” the sites where it has been working and to finish work that would otherwise pose a safety hazard to workers or the public.

Opponents of the project hailed Loyzim’s order and called it a major blow to NECEC’s efforts to build the corridor.

“This is great news for Maine people and our environment,” said Pete Didisheim, advocacy director for the Natural Resources Council of Maine. “This project was fatally flawed from the very beginning.”

“The people of Maine have spoken; thankfully, Commissioner Loyzim has heard them loud and clear,” said Tom Saviello, the lead petitioner on the referendum question. “It’s time for CMP (Central Maine Power, which formed NECEC to build the transmission line) to pack up and go home.”

“CMP’s actions since election day have been abhorrent, so this suspension is critical,” said Sandi Howard, director of the group No CMP Corridor.

Thorn Dickinson, president and CEO of NECEC, was disappointed by Loyzim’s order and said he saw no need for the DEP to suspend the permit since the NECEC voluntarily chose to halt construction on Friday.

“The NECEC has gone to great lengths to mitigate the environmental impacts of the project affecting only a thousand acres of land while committing to preserve 40,000 acres,” Dickinson said in a statement Tuesday night. ” … Moreover, and perhaps most importantly, there has been no change in the real and serious need for this project to address climate change – which the MDEP, after thoroughly analyzing the environmental impacts and alternatives to the project, correctly concluded presents the ‘single greatest threat to Maine’s natural environment.'”

The developers “remain committed” to building the corridor and bringing in cleaner hydropower to New England, he said, and they will press their case arguing that the referendum is unconstitutional in a Maine courtroom next month.

Mills’ office did not respond to requests for comment Tuesday night.

Loyzim’s ruling came hours after a group of 50 Maine lawmakers urged Massachusetts Gov. Charlie Baker to “honor and respect the vote of the people of Maine” and do what he can to terminate the New England Clean Energy Connect project and pursue other options.

The request, contained in a letter to Baker, references the Nov. 2 Maine ballot question passed by 60 percent of Maine voters that would ban transmission lines such as the NECEC project in the Upper Kennebec region.

“As a bipartisan group of lawmakers representing regions throughout Maine,” the letter states, “we discourage Massachusetts from proceeding with this project after the people of Maine delivered a stunning rebuke of the NECEC.”

The letter’s signers are overwhelmingly Democrats, along with two independents and a few Republicans. Baker is a Republican. Baker’s media office didn’t respond to a request for comment sent via email Tuesday.

Two days after the Nov. 2 election, however, Baker said he had been talking with officials in his administration and Avangrid, the parent company of Central Maine Power and NECEC Transmission, about “what the next move here might be.”

Asked by The Boston Globe if he thought the project was effectively dead, Baker replied, “No, I don’t see it as dead.”

In 2016, Baker signed a landmark bill that required Massachusetts utilities to negotiate contracts for 1,200 megawatts of hydroelectric power. That resulted in a deal with Canadian utility Hydro-Quebec for power from a transmission line through New Hampshire, which was subsequently rejected in 2018 by an agency in that state. After that, the Massachusetts utilities pivoted to the NECEC project, which officials say could fill 17 percent of the state’s electricity demand.

But project opponents in Maine say the Bay State and its utilities should have pursued other options. Not mentioned in the letter, but often referenced, is a proposal to bring hydropower from Quebec through Vermont, but underground and underwater instead of over land. The Vermont option was among those considered by Massachusetts, but apparently it was rejected because it was deemed too costly.