The American Booksellers Association is asking the Justice Department to investigate the book price war that broke out last week between three of the nation's top retailers: Wal-Mart, Amazon.com and Target. In a letter to the Justice Department's Antitrust Division dated today, the independent booksellers group wrote that the three companies' actions "constitute illegal predatory pricing that is damaging to the book industry and harmful to consumers."

The price war started when retail giant Wal-Mart slashed online prices on top-selling preorder books, including Sarah Palin's upcoming memoir "Going Rogue" and Stephen King's novel "Under the Dome," to $10. Amazon.com matched that price on the same books. Then Wal-Mart went down to $9, and Amazon followed. Then Target jumped into the fray.

Right now Wal-Mart is offering the books for $8.98 or $8.99 on its website. Amazon has them for $9, and Target has them for $8.99. That's a steep discount from the list price of these books, which range from about $25 to $35.

Here's how the booksellers association sums up the situation in their letter:

The suggested list price set by the publisher reflects manufacturing costs -- acquisition, editing, marketing, printing, binding, shipping, etc. -- which vary significantly from book to book. By selling each of these titles below the cost these retailers pay to the publishers, and at the same price as each other, and at the same price as all other titles in these pricing schemes, Amazon.com, Wal-Mart, and Target are devaluing the very concept of the book. Authors and publishers, and ultimately consumers, stand to lose a great deal if this practice continues and/or grows.

What's so troubling in the current situation is that none of the companies involved are engaged primarily in the sale of books. They're using our most important products -- mega bestsellers, which, ironically, are the most expensive books for publishers to bring to market -- as a loss leader to attract customers to buy other, more profitable merchandise. The entire book industry is in danger of becoming collateral damage in this war.

The book price war is part of a broader ecommerce battle between the companies. Wal-Mart and Target, two of the nation's biggest brick-and-mortar retailers, trail Amazon in online sales, and are working to gain ground. Amazon, meantime, is steadily broadening its product selection to include all kinds of merchandise, which encroaches on Wal-Mart and Target turf.

The booksellers association singles out Amazon — and its policy of pricing electronic books for its Kindle reader at $9.99 — as the original source of the problem.

From the letter:

It's also important to note that this episode was precipitated by below-cost pricing of digital editions of new hardcover books by Amazon.com, many of those titles retailing for $9.99, and released simultaneously with the much higher-priced print editions. We believe the loss-leader pricing of digital content also bears scrutiny.

Representatives of the Tarrytown, N.Y.-based American Booksellers Association, Amazon, and the Justice Department couldn't immediately be reached for comment.

Follow my updates on Twitter.