New England utility Eversource Energy is threatening to take legal action against the Environmental Defense Fund (EDF) over what it said are “false and misleading statements” about the utility’s natural gas pipeline scheduling practices from 2013-2016.

In a cease and desist letter sent Monday, Eversource General Counsel Gregory Butler told EDF to withdraw research it published earlier this year that found Eversource and fellow New England utility Avangrid routinely released unused contracted pipeline capacity too late in the day for it to be picked up on the secondary market. The EDF researchers claimed that this practice, partly because of the region’s pipeline constraints, cost customers an estimated $3.6 billion from 2013 to 2016.

Butler said Eversource was following state regulations designed to ensure reliability for its customers and that the utility “is not permitted to, and does not, profit from higher prices on natural gas or other fuels used to generate electricity, and has no incentive to increase prices.”

EDF’s claims “are irreparably harming the reputation of Eversource Energy. You have repeatedly published assertions drawn from the so-called study…that are unsupported by fact,” Butler said. Claims “that Eversource has intentionally withheld gas pipeline capacity from the wholesale power market in order to profit from higher electricity prices are patently false.”

Eversource said it is prepared to take legal action if EDF does not retract the claims, Butler said. “This is an extraordinary step we are taking on behalf of our employees and customers because we are so deeply concerned and offended about the serious and regrettable false narratives that EDF continues to perpetuate,” he wrote.

EDF has said the scheduling practices it observed fell within the utilities’ contractual rights but pointed to a “need to consider improvements to market design and regulation.”

The EDF claims have created a legal headache for Eversource, which was named in a class action lawsuit filed in a U.S. District Court last month. That lawsuit, which appeared to draw from the environmental organization’s research, accuses the utility of market manipulation and violating antitrust laws.