Authorities in France have blocked the registration of some new Daimler Mercedes cars in an escalating row over the German company’s use of a banned air conditioning coolant. New Mercedes A-Class, B-Class and SL cars assembled since June 12th have been refused registration, even though German authorities have approved them, a Daimler spokesman said.

EU sources suggest that Paris officials had blocked the registration because the cars contained a coolant which is not permitted in the EU. In September, Daimler said that HFO-1234yf, the only air conditioning coolant on the market that conforms to a new EU directive on greenhouse gases, could be the primary source for a vehicle fire. Daimler and its rival Volkswagen are both developing expensive carbon dioxide-based air conditioning systems in order to avoid what they say is a fire hazard posed by HFO-1234yf, which emits poisonous hydrogen fluoride gas when it burns.

Daimler has taken a firm stance and is violating the EU directive by continuing to exclusively use the non-flammable R134a, which the EU has banned because of its potential for pollution. German authorities had extend a permit previously granted to Daimler’s cars to its new models.

General Motor's European unit, Opel, began installing HFO-1234yf-based systems in its Mokka model at the start of the year. Opel says it has found no evidence in crash tests on its new SUV that the air conditioning refrigerant could catch fire in a collision and release toxic fumes.