Germany's main automobile club, a trusted national institution, is under pressure after it emerged that the number of people who voted on the nation's favorite car was inflated.

ADAC says it is Europe's biggest auto club with more than 18 million members. It says communications chief Michael Ramstetter has quit after admitting the number of votes given last year was manipulated — but not the ranking.

Volkswagen's Golf was the winner of the vote.

Horst Seehofer, the leader of one of Germany's governing parties, urged ADAC on Monday to explain the situation fully. He also said he favors an independent investigation.

Justice Ministry spokesman Steffen Ruelke said ADAC depends "to a particularly great extent on its members' trust" and should clear up the matter.