The Federal Cartel Office said in a statement that it has begun questioning thousands of third-party traders who sell their goods on Amazon's online platform.
"Amazon's price parity clause - which denies traders the freedom of offering a product cheaper elsewhere - may breach general cartel rules," said office president Andreas Mundt.
"This is particularly the case if restricting a trader's price-setting freedom also hampers competition between different Internet market places," Mundt said.
There was considerable evidence that this was the case, the cartel office chief said.
Amazon is already under fire in Germany over allegations it mistreats its temporary workers, many of whom are foreign.