The association of German book sellers accused Amazon and its subsidiary Audible on Monday of building a monopoly in the audio book business as it lodged complaints with the German competition authority and the European Commission.

The association said in a statement that Amazon and Audible were abusing their dominant market position to force publishers to accept “unreasonable conditions” for the marketing of audio books.

It said more than 90 percent of all downloads of audio books in Germany were made via the Audible or Amazon sites, or via the iTunes store, which is exclusively supplied by Audible.

“The business model of Amazon and Audible is aimed at destroying the excellent book trade structure in Germany.

These companies are avowedly on the way to establish a monopoly,” said association head Alexander Skipis.

Amazon did not immediately respond to a request for comment. The European Commission said it would assess the complaint, noting it worked closely with national competition authorities like the one in Germany on antitrust matters.

The German association said its complaint meant it was now formally a party to ongoing European antitrust proceedings against Amazon.

In June, the European Commission opened an investigation into Amazon’s ebook business, examining whether clauses in its contracts prevent publishers from offering more favourable deals to competitors.

ebooks are a fast-growing industry and Amazon, which popularised the product, is Europe’s biggest player.

The company could be fined up to 10 percent of its global turnover if found guilty of breaching EU rules.

The investigation is one of two against Amazon. It is also in the European Commission’s crosshairs for deals with Luxembourg which allow it to pay extremely low taxes.