The Federal Trade Commission sued Amazon, alleging the company used manipulative tactics for years to trick users into subscribing to Amazon Prime without their knowledge, and then made it close to impossible to cancel these subscriptions.

“Amazon tricked and trapped people into recurring subscriptions without their consent, not only frustrating users but also costing them significant money,” FTC Chair Lina Khan said in a statement.

The lawsuit alleges that Amazon used “manipulative, coercive, or deceptive user interface designs known as dark patterns” to disguise its auto-renewal process and trick users into remaining Prime subscribers. It details a “four-page, six-click, fifteen-option cancellation process” known internally at Amazon as “the Iliad Flow,” after Homer’s epic war novel.

“Amazon leadership slowed or rejected changes that would’ve made it easier for users to cancel Prime because those changes adversely affected Amazon’s bottom line.”

Amazon dismissed the suit as being “false on the facts and the law.”

“By design we make it clear and simple for customers to both sign up for or cancel their Prime membership,” a spokesperson said.

“We look forward to proving our case in court.”

Amazon Prime costs US$169 a year (A$204), and boasts 200 million worldwide users, meaning the scope for this lawsuit is large. Phone operator Vonage settled a similar “dark patterns” suit with the FTC by paying $100 million.