By David Shepardson

WASHINGTON (Reuters) -The U.S. Federal Trade Commission on Wednesday accused Amazon.com of enrolling millions of consumers into its paid subscription Amazon Prime service without their consent and making it hard for them to cancel, the latest action by the agency against the ecommerce giant in recent weeks.

The FTC sued in Amazon in federal court in Seattle, alleging that "Amazon has knowingly duped millions of consumers into unknowingly enrolling in Amazon Prime." The FTC said Amazon used "manipulative, coercive or deceptive user-interface designs known as 'dark patterns' to trick consumers into enrolling in automatically renewing Prime subscriptions."

The lawsuit is one of several actions taken by President Joe Biden's administration intended to rein in the outsized market power of Big Tech firms as it tries to increase competition to create greater consumer protection.

The FTC said Amazon Prime is the world's largest subscription program, generating $25 billion in revenue annually. It offers fast, free shipping on millions of items, various discounts and access to movies, music and television series, as well as other benefits. Prime members in the United States pay $139 per year and drive much of Amazon's sales volume. Prime has more than 200 million members worldwide.

The FTC said that "one of Amazon's primary business goals - and the primary business goal of Prime - is increasing subscriber numbers."

The lawsuit said that under substantial pressure from the FTC, Amazon changed its cancellation process in April but that "violations are ongoing" and that it still "requires five clicks on desktop and six on mobile for consumers to cancel from Amazon.com."

The agency is seeking civil penalties and a permanent injunction to prevent future violations.

Amazon's shares were down 0.9% in midday trading.

The company did not immediately respond to a request for comment.