Amazon announced on Monday that it was expanding its Amazon Music offerings so that users could stream music for free on their iPhones, iPads, Android devices, and Amazon's Fire TV products, as well as online.

The company said in a blog post that customers without a Prime membership or subscription to Amazon Music Unlimited could now access ad-supported music for free. Previously, this was available only to people using Echo devices.

Investors on Wall Street seemed to think the announcement spelled bad news for Spotify, the music-streaming market leader, whose shares dropped by 4.9%, to $140.26.

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Amazon is expanding free music-streaming to its users without a Prime membership, Amazon Music Unlimited subscription, or Amazon Echo. It may be gunning for Spotify's 248 million-strong user base.

The company published a blog post on Monday detailing what non-paying users could now listen to on Amazon Music through their iPhones, iPads, Android devices, and Amazon's Fire TV products, as well as online.

"Customers who do not yet have a Prime membership, or a subscription to Amazon Music Unlimited, can now listen to an ad-supported selection of top playlists and thousands of stations for free on their favorite devices," the post said.

The company offers a few payment tiers for its music-streaming customers. Amazon Prime members have access to more than 2 million ad-free songs. By upgrading to Amazon Music Unlimited — $8 a month for Prime members and $10 for non-Prime members — users have unrestricted access to the platform's music library.

Previously, the company offered a free, ad-supported version of its music service only for Alexa users on Echo devices.

Monday's announcement seemed to suggest that the company is looking to hook some of Spotify's millions of customers. The popular music-streaming service's latest report said it had 113 million subscribers who pay $10 a month, as well as a larger body of 248 million monthly active users.

But Spotify's free, ad-supported tier is still more developed than Amazon Music's, allowing users to create playlists and play music on demand from their laptops and desktops.

Wall Street reacts

Spotify shares fell by 4.9%, to $140.26, on Monday as investors reacted to the renewed competition from Amazon.

Spotify leads the market in music streaming, outpacing Apple Music in number of subscribers. Last month, the company beat analyst estimates on the number of its paid users and turned a surprise profit.

But Amazon and Spotify may have more challenges to contend with as other companies enter the music-streaming market. The Financial Times reported on Sunday that ByteDance, the Chinese company behind the video app TikTok, was also in talks to launch its own music-streaming service.