NEW YORK (AP) — The book price wars are no longer just for pre-orders.

Amazon.com was offering hardcovers of John Grisham's 'Ford County' and Barbara Kingsolver's 'The Lacuna' for just $9 on Tuesday, the official release date for both books. Hardcovers generally have a list price of $24 or higher.

In mid-October, Walmart.com announced dramatic discounts for pre-orders of 'Ford County,' Sarah Palin's 'Going Rogue' and other popular November publications. Wal-Mart.com initially charged $9 for the books, a price quickly matched by Amazon.com, then dropped to $8.98 by Wal-Mart.com.

Authors, publishers and rival booksellers worry that cutting the price so low will harm competition and force down the cost of books overall, leading to a reduction in author advances.

On Tuesday, Walmart.com was selling 'Ford County' for $12 and 'The Lacuna' for $13.50. Another price cutter, Target.com, was selling 'Ford County' for $15 and 'The Lacuna' for $18.89.