SAN FRANCISCO — More than 450 antiquarian book dealers in at least 26 countries pulled their books off an Amazon subsidiary on Monday, an impromptu protest after the site abruptly said it would drop all sellers from several nations.

The flash strike against AbeBooks, which removed over 2.5 million books from the marketplace, is a rare concerted action by vendors against Amazon, which depends on third-party sellers for much of its merchandise and revenue. The protest arrives as increasing attention is being paid to the extensive power that Amazon wields as a retailer — a power that is greatest in books.

The stores are calling their action Banned Booksellers Week. The protest got its start after AbeBooks sent emails last month to booksellers in countries including South Korea, Hungary, the Czech Republic and Russia to say that it would no longer “support” them. “We apologize for this inconvenience,” the company said.

As the news spread, even unaffected dealers were surprised and angered. AbeBooks, together with Amazon itself, is by far the biggest international marketplace for secondhand and rare books.