An association of independent booksellers is asking the U.S. Justice Department  to investigate Target, Wal-Mart and Amazon.com for what it believes is illegal, predatory pricing.

A book pricing war broke out among the mega-retailers in the past week. All three are now selling new hardcover bestsellers for about $9. The American Booksellers Association estimates the retailers are losing as much as $8.50 per sale in an effort to win control of the market.

"Authors and publishers, and ultimately consumers, stand to lose a great deal if this practice continues and/or grows," the association said in a letter Thursday. "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 ... 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."