Clifford Chance (CC) has been appointed by Amazon to advise on its antitrust investigation by the European Commission, Legal Week can reveal.

The commission opened an investigation into the online retailing giant's e-book business last Thursday over concerns that its contracts with publishers prevented competition from alternative e-book providers.

CC is fielding a team of lawyers headed by the chair of its antitrust group, Thomas Vinje, who is based in its Brussels office. The magic circle firm's lawyers are working with Amazon's in-house legal team, which is being led by senior vice president and general counsel David Zapolsky in Seattle.

The investigation of Amazon was prompted by complaints by the German Publishers & Booksellers Association to the German competition authorities last June.

The association has turned to Frankfurt-based firm Commeo, which is advising on its submissions to the European Commission with a team led by partner Stephanie Pautke.

European Union commissioner in charge of competition policy Margrethe Vestager said: "Amazon has developed a successful business that offers consumers a comprehensive service, including for e-books. Our investigation does not call that into question.

"However, it is my duty to make sure that Amazon's arrangements with publishers are not harmful to consumers by preventing other e-book distributors from innovating and competing effectively with Amazon."

Amazon is already being investigated over its tax affairs by the commission alongside fellow US companies Apple and Starbucks. That investigation is at an advanced stage.

In 2004 CC also advised Amazon on its first acquisition in China, Joyo.com, which sells books, audio and video products.

Its appointment on the Brussels case is a boon for the firm's competition practice after losing several big names last year. CC's EU head of public policy, Oliver Bretz, left to set up a competition law boutique in 2014, consultant and Hong Kong head of competition Stephen Crosswell exited for Baker & McKenzie and Johan Ysewyn left to join Covington & Burling.

There have been several competition investigations of big technology companies by the European Commission in recent years. In April it filed complaints of anti-competitive behaviour against Google. The internet search business instructed Allen & Overy (A&O) and Cleary Gottlieb Steen & Hamilton to defend it in that case.

Most famously, the commission imposed a record fine of €561m (£484m) on Microsoft in 2007 for refusing to give rivals information required to make their systems compatible with Windows and by tying Windows Media Player into its operating system.

In that case A&O represented the original complainant, Sun Microsystems, while White & Case, Covington & Burling and Brussels firm Van Bael & Bellis advised Microsoft.

Amazon did not respond to requests for comment, while CC declined to comment.