The battle over the Environmental Protection Agency’s (EPA) plan to repeal an Obama-era regulation has been reignited.

The Sierra Club, Environmental Defense Fund and Center for Biological Diversity sued EPA on Tuesday to prevent the agency from repealing regulations on refurbished truck engines, called glider kits.

Their suit comes days after the House Committee on Science Space and Technology launched an investigation into potential collusion between lobbyists and EPA officials to keep regulations in place.

The committee obtained emails suggesting Volvo and the Truck and Engine Manufacturers Association worked with top EPA officials at the National Vehicle and Fuel Emissions Laboratory in Ann Arbor, Michigan, to put together a report on emissions from glider kits.

Emails and the involvement of auto lobbyists in procuring vehicles to test “raise serious questions as to the objectivity and legitimacy of the [EPA] study” that has been held up by glider opponents, including Volvo, as evidence of why refurbished engine sales should be limited.

Glider kits are trucks with refurbished engines fitted into new chassis. The glider industry sprang up as truckers looked for an alternative to new trucks that had to comply with ever-stricter federal regulations.

The Obama administration took action in 2016 to close what’s described by environmental activists as a “loophole” by reclassifying gliders as new vehicles, despite the fact they are refurbished engines. The Clean Air Act only gives EPA authority to regulate new vehicles.

EPA regulations limited glider sales to 300 a year, crippling the industry. Glider sales hit 10,000 vehicles in 2015, according to EPA estimates.

Environmentalists argue repealing regulations on glider kits would allow more harmful emissions into the air and harm human health, despite gliders only being a small part of truck sales. Activists have, rather ironically, sided with automakers who make and sell new engines that compete with gliders.

Volvo, Daimler and other major truck manufacturers and their lobbying arms oppose lifting limits on glider kit sales. Gliders are about 25 percent cheaper than buying a truck with a new engine, which eats into new truck sales.

Glider makers did not challenge the Obama administration’s rule in court, but Fitzgerald, a glider company, petitioned the Trump administration in mid-2017 to repeal limits on glider sales.

EPA is still working on finalizing its repeal plan, but the agency said it would not enforce limits on glider sales.

EPA’s no enforcement announcement came on former Administrator Scott Pruitt’s last days in office. Pruitt resigned in early July amid a flurry of investigations into alleged ethics violations. Andrew Wheeler, Pruitt’s deputy, took over as acting administrator.

EPA’s plan to repeal glider regulations has been hampered by bureaucratic delays, including being sent back to the agency from the White House. Now, environmentalists are suing to keep glider regulations in force.

“The EPA’s decision to halt the enforcement of this rule endangers the health and safety of American families and our climate,” Sierra Club counsel Joanne Spalding said in a statement upon filing suit against EPA.

“We are suing Wheeler and the EPA to stop their attempt to disregard established law and processes as they seeks to ransack climate and public health safeguards,” Spalding said.

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This article originally appeared in The Daily Caller