Amazon has banned a book that provides the code needed to 3D print a handgun.

"The Liberator Code Book: An Exercise in the Freedom of Speech," appeared on Amazon's website on August 1. The company said it dropped the $20 book on Wednesday because it violated Amazon's content guidelines, but it would not offer further details.

"Code is speech," the apparent author, "CJ Awelow," wrote in a brief description on Amazon, echoing the legal argument made by the organization behind the code. "Proceeds will be used to fight for free speech and the right to bear arms."

The company's decision to drop the 584-page book, while continuing to offer books like The Anarchist's Cookbook and a United States Army field guide to improvised munitions, represents the latest twist in an ongoing legal fight over 3D printed firearms.

The issue erupted in 2013, when Cody Wilson, a self-described anarchist who founded the gun-rights organization Defense Distributed, posted the code needed to 3D-print a handgun called the Liberator. The US State Department soon sent Wilson a cease and desist letter, ordering him to remove the instructions from his website.

Wilson sued the agency 2015, claiming it was infringing on his First and Second Amendment rights. The government settled the case in June, and Wilson planned to publish the code needed to create a variety of firearms on August 1. A federal judge granted a temporary national injunction on July 31 barring him from doing so.

Amazon's ban speaks to a broader issue facing platforms such as Facebook and retailers such as Amazon as they attempt to police the content appearing on their sites. Some critics of Amazon's decision took to social media to note that the company offers a wide range of other controversial books, including Mein Kampf.

"This is one [sic] again a huge blow to our first amendment. If you want change, act now," Defense Distributed tweeted Wednesday night.

Wilson envisions Defense Distributed as a place for anyone to share or download blueprints for firearms, leading to new types of weapons.

"I don't believe that access to information is ever tremendously negative or a bad thing," Wilson told CNN in a recent interview. "People can use information for bad things. But this isn't a justification to what, stop a publisher from speaking."

Steve Almasy and Abigail Brooks contributed to this report.