Spotify and Apple are at war

Spotify is accusing Apple of abusing its power.

Spotify sent a letter to Apple's general counsel in May accusing the company of using its iPhone and iPad App Store platform as a "weapon to harm competitors," Recode's Peter Kafka reports.

"This latest episode raises serious concerns under both US and EU competition law," says the letter, according to Recode.

Apparently, Spotify has also been shopping the letter with Congressional staff in Washington DC, too, a move that signals that Spotify is trying to drum up support for a legal campaign.

Spotify's complaint concerns how Apple makes money off of the App Store. Traditionally, Apple takes a 30% cut of transactions initiated through iPhone apps, although it changed its fee schedule slightly for subscription services earlier this year.

That means that Spotify would pay Apple $3 per month when someone pays for a $10 per month subscription through the iPhone app. So Spotify raised its price for iPhone signups to $13 per month.

More recently, Spotify tried to get its users to sign up for its service outside of the Apple app by offering discounts - but that made Apple angry. Spotify's letter says that Apple threatened to block the Spotify app on the App Store in response.

What makes this potentially anticompetitive is that Apple's music service, Apple Music, is in direct competition with Spotify - and Apple reportedly rejected a new version of Spotify's app for iPhones and iPads.

Senator Elizabeth Warren, a Democrat from Massachusetts, attacked Apple in a speech on Wednesday, saying that it and other tech companies, like Google and Amazon, have amassed too much power. With regards to Apple, she said:

"While Apple Music is easily accessible on the iPhone, Apple has placed conditions on its rivals that make it difficult for them to offer competitive streaming services. The FTC is investigating those issues and deciding whether to sue Apple for antitrust."

The first murmurs about Spotify chafing under Apple's platform surfaced about a year ago.

Spotify has 30 million paying subscribers and Apple Music has 15 million.

Spotify and Apple did not return requests for comment.