Amazon.com officials did not respond to queries about this story.

Some commenters have even urged a boycott of e-books costing more than $9.99. "It's important that OLD and NEW Kindle folk DO NOT purchase anything over $9.99," wrote C.S. Stein in a post. "This was one of the big selling points for me and I will not be bait and switched. Keep together, all!"

Another person, using the handle "Bayou Banker," posted a comment Wednesday about his disappointment on pricing of e-books. "I just ordered a Kindle 2 and THEN discovered all [e-books] are not $9.99 as they would have you believe. I intend to complain and will not order anything over $9.99."

To be sure, the forum has links to free and discounted books, partly to urge boycotters to avoid paying high prices.

One commenter with the name of "Knipfty" has posted of how many Kindle e-books are available for purchase, with the amount and percentage of those priced more than $9.99.