Fiat's plan to build a European car giant with Chrysler and GM's German unit, Opel, began to hit obstacles yesterday 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).

According to a document obtained by the Financial Times, Frank-Walter Steinmeier, Germany's vice-chancellor, said Opel's future owners might have to base the company there – one of 14 criteria the foreign minister would use to evaluate any offer.