Austria's competition authority has begun investigating whether Amazon is exploiting its market dominance in relation to other retailers that use its website as a marketplace, it said on Thursday.
This follows a similar move by German authorities, which announced an investigation in November.
European regulators have been taking a tough line on US tech giants like Google and Facebook, while the European Commission is also looking into Amazon's dual role as retailer and marketplace.
The Austrian regulator said it would examine terms and conditions under which the US online giant grants Austrian vendors access to its marketplace.
"There is a suspicion that Amazon puts other retailers on a disadvantage on its marketplace, thereby trying to favour its own offerings," it said in a statement.
Amazon Assures Cooperation
Amazon said it does not comment on ongoing proceedings but would "cooperate fully with the Austrian competition authority".
The regulator said unfair trade practices which might be considered include abrupt termination of seller accounts, obligations to disclose purchase prices and jurisdiction clauses that complicate taking legal action.
"The outcome might be commitments, an application for a fine or an application for termination of infringements to the cartel court," director general Theodor Thanner said.
Austrian retailers filed a complaint against the US firm with the authority in December.
They said Amazon could in theory see the prices listed by retailers on its platform, undercut their prices and attract all that business in the long run.
Retailers make up nearly 60% of bought items on the Amazon site and their revenues grow twice as fast in the European Union as Amazon's own sales, the US firm says.
Nearly every Austrian online shopper has made at least one purchase on Amazon, Austrian Retail Association's data show.
