Clifford Chance have become the latest law firm in a growing list of big players consulted by Amazon on their growing issue of an antitrust investigation into the distribution of their popular e-books.

Firms already consulted by Amazon on the issue are understood to include: Osborne Clarke, Olswang, CMS Cameron, McKenna, Herbert Smith Freehillds & Latham & Watkins. Clifford Chance have so far refused to comment on the scale of their involvement in the case.

The European Commission decided to launch an investigation in Amazon's distribution of their e-books last week following suspicions that certain clauses present within the contracts held with their publishers may infringe competition laws.

Clauses present within the contracts require publishers to inform Amazon if more favourable terms are being offered to their competitors and then offer them the same deal.

EU competition policy commissioner Margrethe Vestager says: “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. Our investigation will show if such concerns are justified.”