Fiat’s plan to build a European car group with Chrysler and GM’s German unit, Opel, began to hit obstacles on Monday as Berlin issued a string of conditions for any Opel buyer, and dissident Chrysler creditors said a sale to Fiat would be “patently illegal”.

The moves came as Sergio Marchionne, Fiat’s chief executive, met government and union officials in Berlin in the first round of his campaign to secure political backing by the end of this month for a car group with up to 7m in annual sales and combined revenues of €80bn ($107bn).