Daimler said that it would take a one-time charge of hundreds of millions of euros against the upcoming quarter's earnings to deal with the new accusations, but it disputed the government regulator's determination that the software in question was illegal.

Daimler plans to formally object to the claims.

Today, the Daimler vehicles in question are Mercedes-Benz-brand vehicles that are only sold in the EU. According to a WSJ source, the problem relates to a coolant thermostat in the cars that protects parts of the engine. The related software is found on vehicles made between 2012 and 2015.

The type of coolant thermostat used on the diesel vehicles in question is generally found on cars with catalytic converters that don't use selective catalytic reduction, an emissions-reduction technique that uses urea to reduce nitrogen oxides to less harmful forms. But the GLK 220 CDI 4MATIC Mercedes-Benz models that must be recalled do appear to use selective catalytic reduction.

The latest regulatory action is reminiscent of the accusations lobbed against VW Group in 2015, where the U.S. EPA accused the automaker of including illegal software on its diesel vehicles to ensure that the diesels would pass emissions limits imposed by the US.