US online retailer Amazon's pricing policy for its third-party traders in Germany is being investigated by antitrust authorities.
A clause bans traders signed up to its Marketplace platform from offering products elsewhere for cheaper - including in their own online shops.
The Federal Cartel Office is to question 2,400 people who sell their products directly to Amazon customers.
It said the company may be breaching antitrust rules.
"Amazon's price parity clause - which denies traders the freedom of offering a product cheaper elsewhere - may breach general cartel rules," said the FCO's head Andreas Mundt.
"This is particularly the case if restricting a trader's price-setting freedom also hampers competition between different internet market places."
If the e-commerce giant is found to be in breach of antitrust rules, it could be forced to drop the clause.
Amazon declined to comment to the BBC.
The inquiry comes just days after a TV documentary showed Amazon's seasonal workers in Germany being harassed by security guards.
Last week, German authorities asked the retailer to explain the documentary, filmed by state broadcaster ARD, which said employees' rooms were searched, they were frisked at breakfast and constantly watched.
Employment Minister Ursula von der Leyen said some employment agencies could lose their operating licences.
In a statement, Amazon said it would follow up complaints.