Investigations into the Volkswagen emissions scandal continue to widen.

The Environmental Protection Agency today issued a second “notice of violation” of the Clean Air Act to Volkswagen, Audi, and Volkswagen Group of America. Porsche and Porsche Cars North America also received this notice.

The notice of violation alleges that VW developed and installed a defeat device in certain VW, Audi and Porsche light-duty diesel vehicles equipped with 3.0 liter engines for model years 2014 through 2016 that increases emissions of nitrogen oxide up to nine times EPA’s standard.

The vehicles covered by the notice are the diesel versions of the 2014 VW Touareg, the 2015 Porsche Cayenne, and the 2016 Audi A6 Quattro, A7 Quattro, A8, A8L, and Q5.

These alleged violations are in addition to the notice of violation issued on Sept. 18 and the ongoing investigation by EPA alleging a defeat device on certain 2.0 liter engines for model years 2009 through 2015 vehicles.

Both the EPA and the California Air Resources Board (CARB) have initiated investigations based on Volkswagen’s alleged actions. The notice of violation covers approximately 10,000 diesel passenger cars already sold in the United States since model year 2014.

On Sept. 25, CARB sent letters to all manufacturers “letting them know we would be screening vehicles for potential defeat devices,” Richard Corey, executive officer of the California Air Resources Board, said in a statement. Since then, CARB, EPA, and Environment Canada have continued test programs on additional diesel-powered passenger cars and SUVs, he said.

“These tests have raised serious concerns about the presence of defeat devices on additional VW, Audi, and Porsche vehicles,” said Corey. Both CARB and EPA will continue to conduct a “rigorous investigation that includes testing more vehicles until all of the facts are out in the open,” he added.

Volkswagen may be liable for civil penalties and injunctive relief for the violations alleged in the notice of violation. The EPA said that Volkswagen will have an opportunity to respond to the allegations contained in the notice of violation.

In a statement on its website, Volkswagen denied the allegations. “Volkswagen AG wishes to emphasize that no software has been installed in the 3-liter V6 diesel power units to alter emissions characteristics in a forbidden manner,” the company said. “Volkswagen will cooperate fully with the EPA clarify this matter in its entirety.”