The case centres on a contract Amazon wants POD book publishers to sign that mandates books are printed at its own facilities or, where sellers wish to use an alternative service, a handful of copies of each title are printed and shipped to Amazon beforehand.

Amazon responded to the allegations, which are being heard in the US district court of Maine, saying that printing POD books through its own Booksurge facility is not the only option open to publishers wishing to sell through its site and that Booklocker.com failed to show any evidence of how what it described as "unfair trade practices" had injured its business.

Booklocker.com has now filed a memorandum maintaining that Amazon's structure has now been rigged so that only having Amazon print POD titles is a viable economic option and asks that the court lets it acquire evidence from Amazon into this.

It argues Amazon's assertion that printing at its own facilities enables operational efficiencies is redundant as it already ships books directly from the POD presses to consumers without routing them through fulfilment centres to match them with other goods purchased by the same buyer.

Booklocker.com also alleges that several other POD publishers have capitulated to Amazon's demands and that its own customers hold a dim view of the quality of Amazon's Booksurge POD facility, claiming that with Amazon's 70% market share, it is harming fair competition.