Jeep FCA shares were briefly halted after plummeting nearly 16% in response to the Environmental Protection Agency accusing the automaker of using emissions cheating software.

The EPA said the software allowed excess diesel emissions in just over 100,000 U.S. trucks and SUVs sold since 2014. The EPA said it believes the software allowed vehicles to generate excess pollution in violation of the Clean Air Act.

FCA shares were down 12% in recent trading.

The EPA alleges that the software was installed in light-duty models of the Jeep Cherokee for the years 2014-2016, as well as Dodge Ram 1500 trucks with 3.0 liter diesel engines sold in the United States.

FCA wrote in a statement that it was "disappointed that the EPA has chosen to issue a notice of violation with respect to the emissions control technology employed in the company’s 2014-16 model year light duty 3.0-liter diesel engines."

"FCA US intends to work with the incoming administration to present its case and resolve this matter fairly and equitably and to assure the EPA and FCA US customers that the company’s diesel-powered vehicles meet all applicable regulatory requirements," the statement continued.

The allegations come amid rising scrutiny by the EPA of automaker emissions after Volkswagen admitted to cheating diesel emissions tests in 580,000 U.S. vehicles. On Wednesday, Volkswagen plead guilty to three felonies as part of a $4.3 billion settlement.

The EPA is also investigating whether the software FCA used can be considered "defeat devices," which are illegal. The software Volkswagen used to cheat emissions tests were considered defeat devices.

FCA wrote in its statement that its diesel engines are equipped with "state-of-the-art emission control systems hardware" to control tailpipe emissions. "FCA US believes that its emission control systems meet the applicable requirements," the company wrote.

In November, there was a class-action lawsuit brought against FCA and engine manufacturer Cummins accusing them of cheating on diesel emissions tests. Both companies said they would fight the lawsuit.

The EPA has for months declined to certify Fiat Chrysler's 2017 diesel vehicles for sale in the United States.