Mercedes-Benz is expressing bewilderment why France continues to impose its blanket certification ban on its A, B, CLA and SL models, despite other brands in its range using the same controversial refrigerant to which Paris takes such exception.

The German automaker uses the r134a refrigerant in its air-conditioning units - a chemical the European Union (EU) and France deem to emit excessively high pollution - but Mercedes claims the Brussels-mandated r1234yf variant can be highly flammable in certain conditions.

"France has accepted every type approval for every [other] type of our Mercedes, including S Class which is also using r134a," a Mercedes-Benz spokesman told just-auto from Germany. "So it is a little bit difficult [to] understand.

"All other Mercedes models in our range are accepted in France - it is really a big question. We did not receive any answer from France - that is really surprising. We have no reason why France has acted this way."

The German automaker is currently working on an alternative, CO2-based refrigerant to r134a but this will not be ready until around 2017, with even that target viewed as "ambitious."

The issue is mired in internal French politics however, with the Environment Ministry overruling a decision last week by the Tribunal de Versailles to allow Mercedes certification of its four models.

The Ministry invoked the infamous Article 29 of the EU air-conditioning directive, allowing Member States to refuse vehicle registration for six months where a risk to the environment was involved.

"If these [four] models are not accepted by the European Commission and effectively by the French State, it is because these models do not [conform to] this new legislation from 1 January, 2013," a French Environment Ministry spokeswoman told just-auto from Paris.

"It is a directive applicable to all countries in Europe and not uniquely France. France is the first country to forbid these vehicles. Perhaps France applies it in a vigorous fashion."

The increasing heat of the argument however, is having a concrete effect on the ground with Mercedes France dealers warning they may have to make 1,500 out of 11,000 staff partially redundant as thousands of backlogged orders pile up.

"The present situation is having a disastrous effect on our sales, a situation amplified by our competitors, who are not wasting time in using this argument to improve their own performances and divert our loyal customers," said a letter from Groupement des Distributeurs et Reparateurs president, Jean-Claude Bernard and his senior colleagues sent to French Environment Minister, Philippe Martin.

"This situation is resulting in a completely unfair competitive disadvantage, to which we are incapable of responding and which will profoundly handicap our businesses."

No information was immediately available from the Environment Ministry concerning Mercedes' claim its other models using r134a were allowed to be certified in France.

Mercedes is now consulting its lawyers, but it is not yet clear what action this might entail.