WASHINGTON (Reuters) - Fiat Chrysler Automobiles NV (>> Fiat Chrysler Automobiles NV) and Cummins Inc (>> Cummins Inc.) said on Monday they will fight a class-action lawsuit filed against the companies accusing them of cheating on diesel emissions tests.

On Monday, lawyers representing owners of older 2500 and 3500 Dodge Ram trucks filed a class-action lawsuit in U.S. District Court in Detroit, asserting the companies "conspired to knowingly deceive consumers and regulators of illegally high levels of diesel emissions in their vehicles."

The suit accuses the automakers of fraud, violating the Racketeer Influenced and Corrupt Organizations Act and consumer-protection laws by intentionally misleading the public, concealing emissions levels and illegally selling noncompliant polluting vehicles.

The suit filed by Seattle lawyer Steve Berman said the emissions catalysts are not durable and do not meet emission standards, and that at times emissions are nearly 10 times legal limits.

The class action suit comes as Fiat Chrysler and Cummins are fighting over the costs of an emissions recall involving a different, newer population of trucks.

Fiat Chrysler said in a statement it "does not believe that the claims brought against it are meritorious" and the company "will contest this lawsuit vigorously."

Cummins spokesman Jon Mills said the lawsuit "has no merit. We are obviously disappointed in the effort to tarnish our image and we plan to vigorously defend ourselves."

The suit covers owners of 2007–2012 Dodge Ram 2500 and 2007–2012 Dodge Ram 3500 pickup trucks.

Reuters reported on Oct. 10 that Fiat Chrysler and Cummins Inc have been fighting over the $200 million estimated cost for a recall of 130,000 newer 2500 Ram pickup trucks equipped with Cummins diesel engines that could exceed U.S. pollution limits.

The U.S. Environmental Protection Agency and California Air Resources Board have demanded a recall of 2013-2015 model year Ram 2500 pickup trucks with 6.7L Cummins diesel engines because moisture can lead to the deactivation of the selective catalyst reduction system, causing excess nitrogen oxide emissions, Cummins said.

Fiat Chrysler has sued Cummins to recover the $60 million it has spent to date repairing 42,000 trucks at its own expense, a company lawyer said in court documents. Settlement talks are ongoing.

Cummins counter-sued, saying Fiat Chrysler would not cooperate in the recall "for one reason - money" and said the automaker was "holding both Cummins and its own customers hostage."

When the emissions system fails, the warning light goes on and if the vehicle isn't fixed soon the vehicles go into "limp mode" that allow them to only be driven very slowly.

(Reporting by David Shepardson; Editing by Sandra Maler)

By David Shepardson

Stocks treated in this article : Cummins Inc., Fiat Chrysler Automobiles NV