Apple has been going toe-to-toe with Spotify in the subscription streaming service game since last year and it seems things are now going beyond friendly competition.

Spotify has accused the iPhone maker of rejecting its updated iOS from the App Store for anti-competitive reasons.

Writing to Apple's legal team and US congressional staff in Washington DC, Spotify complains that Apple is "causing grave harm to Spotify and its customers."

Its main bone of contention is the strict control Apple has over third-party apps on its iPhone and iPad, with the Swedish company referring to its App Store as a "weapon to harm competitors" and voicing "serious concerns under both US and EU competition law."

According to Spotify's general counsel Horacio Gutierrez – a former Microsoft lawyer – Apple's refusal to approve the update "continues a troubling pattern of behaviour by Apple to exclude and diminish the competitiveness of Spotify on iOS and as a rival to Apple Music.

The accusations come just a few weeks since Spotify opted to remove its option to let people subscribe to its paid service using Apple's payments system.

Spotify had been charging €13 for users availing of that option, a 30% hike on its standard fee to take into account the amount Apple takes for itself on every purchase.

The criticism comes as Apple looks set to edge even further into Spotify's territory by considering a potential takeover bid for Jay Z's music-streaming service Tidal.