PARIS (AP) — Shares in French carmaker PSA Group have tumbled because of a report that as many as 1.9 million Peugeot and Citroen cars may have engines designed to trick diesel emissions tests.

The report in Friday's Le Monde says the company could face up to 5 billion euros ($6 billion) in fines. It says PSA used special devices that programmed engines to vary their emissions levels when being tested.

PSA denied wrongdoing and threatened to file a complaint over the report.

The agency is investigating several car brands sold in France after Volkswagen was found to have cheated on U.S. emissions tests.

PSA said "its vehicles have never been equipped with software or systems" allowing it to deceive tests. Shares were down 4.5 percent to 17.76 euros in Paris.