Word of the problem started spreading across blogs and Twitter on Sunday after Mark R. Probst, the author of “The Filly,” a gay western romance for young adults, posted on his blog that several gay romances, including his, had lost their sales rankings on Amazon. Mr. Probst e-mailed Amazon and got a reply that said the company was excluding “ ‘adult’ material from appearing in some searches and best-seller lists.”

In an interview on Monday, Mr. Probst said he was giving Amazon the benefit of the doubt. “I believe it was an error,” he said. “I don’t think it was anything malicious they were trying to do.”

But other authors were unconvinced that the changes were caused by a simple glitch.

“There are mistakes and there are mistakes,” said Daniel Mendelsohn, an author whose memoir “The Elusive Embrace” lost its sales ranking over the weekend. “At some point in this process, which I don’t understand because I’m not a computer genius, the words gay and lesbian were clearly flagged, as well as some kind of porno tag. I say, do I want my book in anyone’s mind to be equivalent to a porno? And the answer is no.”

Mr. Mendelsohn pointed out that books like “American Psycho,” a novel with sexually and violently explicit content, did not lose its sales rank. He teamed up with others affected by the problem, including the playwright and author Larry Kramer, to start a petition to boycott Amazon. As of Monday afternoon it had attracted more than 18,000 names.

Mr. Kramer said on Monday that he was willing to shelve the boycott for now. But in an e-mail message he wrote: “I don’t think for one second that this was a glitch,” adding, “We have to now keep a more diligent eye on Amazon and how they handle the world’s cultural heritage.”

Image A Twitter screen concerning Amazon. The subject was among the most popular on the site.

Several publishers whose books were affected, including Simon & Schuster, the Penguin Group USA and Houghton Mifflin Harcourt, declined to comment. Calls to a Random House representative were not returned.