NEW YORK — Amazon was sued Wednesday by Federal Trade Commission for what it called a yearslong effort to enroll consumers without consent into its Prime program and making it difficult for them to cancel their subscriptions.

In a complaint filed in the U.S. District Court for the Western District of Washington, the agency accused Amazon of using deceptive designs, known as “dark patterns,” to deceive consumers into enrolling in the program. It said the option to purchase items on Amazon without subscribing to Prime was more difficult in many cases. It also said that consumers were sometimes presented with a button to complete their transactions — which didn’t state it would also enroll them into Prime.

Internally, Amazon called the process “Iliad,” a reference to the ancient Greek poem about the lengthy siege of Troy during the Trojan War.

Company leaders slowed or rejected changes that made canceling the subscription easier, the complaint said. It argued those patterns were in violation of the FTC Act and another law called the Restore Online Shoppers’ Confidence Act.

Launched in 2005, Prime has more than 200 million members worldwide who pay $139 a year, or $14.99 a month, for faster shipping and other perks, such as free delivery, returns and the streaming service Prime Video.

In the first three months of this year, Amazon reported it made $9.6 billion from subscription, a 17% jump from the same period last year.

The FTC also accused the company of attempting in several instances to hinder the agency’s investigation into Prime, which began in 2021.