Beata Zawrzel/NurPhoto/Getty Images

An Amazon Prime subscription is a must in my house; we love fast and free shipping for anything from tech gadgets to grocery delivery. But not everyone is the same, and we can also appreciate when someone declines, cancels, or removes their consent to something -- Amazon, according to the Federal Trade Commission (FTC), cannot.

The FTC accuses the company, which is preparing for Prime Day, its biggest sale of the year, of "knowing failure to address non-consensual subscriptions and cancellation trickery" in the complaint. And if these accusations sound nefarious, it's because they are.

Also: Forget Prime Day. These are the best Amazon Prime alternatives.

In a complaint filed on June 21, the FTC, a US government consumer protection agency, took formal action against Amazon for enrolling customers into its Prime subscription without their consent. It subsequently used manipulative, coercive, and deceptive user interface designs to trick them into automatically renewing their memberships. 

"Amazon tricked and trapped people into recurring subscriptions without their consent, not only frustrating users but also costing them significant money," according to FTC Chair Lina M. Khan. 

Also: Free Prime Day: How to get access to deals for free, even if you're not a Prime member

Dark patterns are part of an unethical technique to design the user interface on websites and mobile apps in a way that manipulates the users to take actions they otherwise wouldn't have taken. These actions tend to benefit the developer or company behind the interface. 

"These manipulative tactics harm consumers and law-abiding businesses alike. The FTC will continue to vigorously protect Americans from 'dark patterns' and other unfair or deceptive practices in digital markets," said Khan.

Also: Amazon to test escrow service in digital money pilot

In Amazon's case, the FTC claims the company designed a deliberately labyrinthine cancellation process. It called it the 'Iliad Flow,' alluding to Homer's epic poem set over 24 books about the decade-long Trojan War. 

The FTC claims Amazon made finding the cancellation flow difficult and then redirected its customers who wanted to cancel through several confusing steps and instead presented offers not to cancel at all, continue their Prime subscription for a discounted price, or turn off the auto-renew feature. According to the complaint, it was only after clicking through these pages that customers could finally cancel their memberships.

Amazon

How to turn your old Fire tablet into an Echo ShowTrade in your old devices for Amazon gift cards. Here's howThe best Amazon tablets: Play with FireAmazon Kindle Scribe review: 7 months later, it's so close to perfect

• How to turn your old Fire tablet into an Echo Show
• Trade in your old devices for Amazon gift cards. Here's how
• The best Amazon tablets: Play with Fire
• Amazon Kindle Scribe review: 7 months later, it's so close to perfect