The New York Times has reported that online book retailer has removed the buy buttons from all active Macmillan titles on its site in a dispute over the pricing of e-books for the Kindle. The move appears to be an escalation in the on-going struggle between and the major book publishers who are concerned that the $9.99 price for Kindle e-books is too low, undervalues its products and may cannibalize print sales. Macmillan titles can only be purchased on the site through used book or third-party resellers.

Macmillan CEO John Sargent had no comment on Amazon's action; Amazon executives could not be reached Saturday morning for comment.

Publishers displeasure with’s $9.99 price for Kindle e-books has been growing along with the popularity of the Kindle, which has also helped to set the price as an unofficial standard as new devices and e-book vendors enter the market. In the wake of the launch of Apple’s iPad device and its content deals with the big publishers, it has been reported that Apple and the publishers have agreed on prices of $12 to $15 for e-books sold through Apple’s forthcoming iBooks Store. So far publishers have declined to discuss their iPad pricing policies.