BookLocker.com, which has a catalogue of around 1,200 POD books, filed a lawsuit on Monday at the US District Court of Maine "to obtain injunctive and monetary relief against Amazon.com, Inc with regard to an anti-competitive tying arrangement".

This turn of events, which could be seen as a David and Goliath tale, follows Amazon's recent attempts to force POD publishers to use Booksurge – its own on-demand printer.

BookLocker's case centres on the allegation that Amazon has threatened POD publishers with loss of access to its direct sales channel unless they use Booksurge as their on-demand printer.

In a statement, BookLocker publisher Angela Hoy said: "It is our opinion that Amazon may be positioning itself to directly print and control every book it sells.

"By forcing publishers to sign their extraordinarily oppressive contract, Amazon gains the power to charge publishers whatever printing and distribution costs it desires."

BookLocker, which currently uses Lightning Source to print its books, admitted that it did not know for certain whether or not Amazon had committed an illegal act, however, it described the online bookseller's actions as "highly suspicious".

Amazon previously issued an open letter arguing that by printing all orders through Booksurge, it could serve its customers more efficiently.

Damien Peachey, head of PR for Amazon.co.uk, said: "We as a company do not comment on ongoing litigation."