Mees: critic of Piëch
He will be replaced by Johan de Nysschen, president of Audi Japan, sources say.
Mees, 53, told writers that the VW Phaeton was not selling because VW underestimated the weakness of the VW brand in the high-end market.
He also stated that Piëch "was an engineer and he wanted to prove that he can build great cars, and he didn't look at the marketing aspect, the brand aspect."
An Audi AG spokesman said Mees was dismissed because he had no plan in place to reverse declining sales.
But a VW spokes-man in Wolfsburg said Mees was fired solely because of his remarks.
Sales through October are down 9.7 percent to 63,388 units.
De Nysschen, 44, already was set to become chief operating officer of Audi of America on January 1.
Mees' comments were made during the US launch of the redesigned Audi A6 sedan in San Francisco, California, on November 8.