Amazon is being challenged by consumer watchdogs in Europe and the US over its use of manipulative "dark pattern" design to promote its Prime service.
The Norwegian Consumer Council (NCC) found that cancelling a subscription required scrolling through six pages and making several complex choices.
It has filed a legal complaint with Norway's consumer protection authority claiming the design breaches EU law.
Amazon rejected claims the process was unfair or difficult.
In the US, consumer watchdog Public Citizen is leading a coalition of groups that is also filing a complaint with the Federal Trade Commission. And consumer groups in France, Denmark, Germany, Greece and Switzerland are also calling for action.
The study from the NCC said that on each of the six pages in the cancellation process, the consumer "is nudged towards keeping their Prime membership".
The pages include yellow warning triangles with an exclamation point inside and buttons containing the text "keep my benefits".
This, it said, is an example of "dark patterns" - which it defines as techniques or features of design that are meant to manipulate users.
The watchdog also spoke to 1,000 Norwegian consumers about their experiences and found that one in four recalled having difficulties unsubscribing from digital content services.
Amazon Prime is a digital subscription service with more than 150 million members globally. It offers free and fast shipping of Amazon products, as well as access to other services such as Prime Video films and TV shows.
In the UK, it costs £79 a year or £7.99 a month.
In a statement, Amazon said it "makes it clear and easy for Prime members to cancel their subscription at any time, whether through a few clicks online, a quick phone call or by turning off auto renew in their membership options".
It added: "Customer trust is at the heart of all of our products and services and we reject the claim that our cancellation process is unfair or creates uncertainty.
"The information we provide in the online cancellation flow gives a full view of the benefits and services members are cancelling."
In 2019, the UK's Advertising Standards Authority ruled that one of Amazon's page layouts was misleading and meant people could easily have signed up for Prime unintentionally.
The NCC's director of digital policy, Finn Lutzow-Holm Myrstad, said: "It should be as easy to end a subscription as it was to subscribe in the first place.
"Amazon should facilitate a good user experience instead of hindering customers and tricking them into continuing paid service they do not need or want."
Previously the watchdog has investigated Google and Facebook over their use of "dark patterns" in the design of their privacy polices.
It found that the documents often hid privacy-friendly options or forced users to take longer to sign up to them, with some settings obscured and pop-ups omitting key information.