Is Amazon.com's clash with publishers over its discount pricing of electronic books entering a new, more high-stakes phase? As VentureBeat reports, books from publishing house Macmillan have gone missing from Amazon's website.

Macmillan is part of a group of major publishers providing digital titles for Apple's new iPad tablet computer. Apple is reportedly letting publishers set higher prices on Kindle e-books ($12.99 and $14.99). Amazon has set a standard of $9.99 for new release e-books — a price that many publishers fear will eat into hardcover sales and lower the value of books in the minds of consumers.

Macmillan imprints include Farrar Straus and Giroux, Henry Holt & Company, and St. Martin's Press.

Amazon declined to comment and Macmillan couldn't immediately be reached.

Update: The New York Times, citing an industry source, reports that Macmillan demanded that Amazon raise the price on e-books to $15, and Amazon is "expressing its strong disagreement by temporarily removing Macmillan books."

That would represent a big escalation of Amazon's battle with publishers, which has until now been going on behind the scenes. It also signals that Amazon will be aggressive in taking on Apple's iPad, which is encroaching on Amazon's Kindle business.

Amazon removed both physical and electronic books from Macmillan (though third party sellers on Amazon still carry some of the titles). That's a pretty dramatic move. It would be interesting to know if Macmillan, one of the country's biggest publishers, was blindsided by this or if it expected Amazon to take action.

Is Amazon making an example of Macmillan, to send a signal to other publishers? Apple is also working with HarperCollins, Hatchette, Simon & Schuster, and Pearson. Many of those publishers have made a policy of holding back e-book titles from Amazon for months after hardcover release.

Update: Macmillan CEO John Sargent, in a letter to authors, illustrators, and the literary community posted on the publishersmarketplace.com website, writes:

This past Thursday I met with Amazon in Seattle. I gave them our proposal for new terms of sale for e books under the agency model which will become effective in early March. In addition, I told them they could stay with their old terms of sale, but that this would involve extensive and deep windowing of titles. By the time I arrived back in New York late yesterday afternoon they informed me that they were taking all our books off the Kindle site, and off Amazon. The books will continue to be available on Amazon.com through third parties.

Under the model that Sargent proposed, most digital titles would be priced between $12.99 and $14.99, and appear on the same day as physical books, with the retailers taking a 30 percent commission. That's essentially Apple's model for e-books on the iPad.

Sargent said he regrets the impasse, but didn't give an indication of backing down. Stay tuned

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