Volkswagen AG denied claims made by the U.S. Environmental Protection Agency (EPA) Monday that the German automaker installed software designed to defeat emissions tests on 2014 to 2016 vehicles with 3.0-liter, six-cylinder diesel engines. The notice issued Monday applies to roughly 10,000 diesel passenger cars sold in the U.S., including a Porsche model.

“The United States Environmental Protection Agency (EPA) informed Volkswagen Aktiengesellschaft on Monday that vehicles with V6 TDI engines had a software function which had not been adequately described in the application process,” the company said in a statement late Monday. “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 also pledged in the statement that it would cooperate with the EPA “to clarify the matter in its entirety.”

In a letter posted on its website, the EPA said it has determined that certain Audi, Porsche and Volkswagen models with 3.0 liter engines were rigged to pass pollution tests. The affected models include the 2014 VW Touareg, the 2015 Porsche Cayenne and the 2016 Audi A6 Quattro, A7 Quattro, A8, A8L and Q5.

"We are surprised to learn this information. Until this notice, all of our information was that the Porsche Cayenne Diesel is fully compliant," Porsche, which is owned by Volkswagen AG, said Monday, adding that it will cooperate fully with authorities.

In September, Volkswagen admitted that it had so-called "defeat devices" on its cars that would reduce emission levels during tests. The automaker revealed that as many as 11 million vehicles carry the cheating software, prompting an investigation from the EPA and the California Air Resources Board.

"VW has once again failed its obligation to comply with the law that protects clean air for all Americans," Cynthia Giles, assistant administrator for the Office of EPA's Enforcement and Compliance Assurance, said Monday, according to CNBC.

"All companies should be playing by the same rules. EPA, with our state, and federal partners, will continue to investigate these serious matters, to secure the benefits of the Clean Air Act, ensure a level playing field for responsible businesses, and to ensure consumers get the environmental performance they expect."

Audi and Porsche are reportedly the source of most of the company’s earnings. Audi posted lower profits in the September quarter citing the costs of developing new models and building factors, but also warned of the impact on future earnings of the emissions scam involving parent Volkswagen AG.

“At the time of reporting, the diesel issue did not have any effect on the forecast for our key performance indicators,” Audi said in its interim report, according to the Wall Street Journal. “Due to the diesel issue, the Audi Group could experience changes affecting the organizational and economic business process.”

Volkswagen shares closed down nearly 3 percent in Frankfurt Monday.