Google and Apple are among the biggest players in the smartphone market. But in a letter to the European Union, chief executives from European companies including Spotify, Deezer and Rocket Internet said the mobile giants are abusing their size within the market, Business Insider reported

While Google and Apple aren’t called out by name, the letter writers specifically highlighted mobile operating ecosystems, app stores and search engines they claim exhibited anti-competitive behaviors. As IDC noted, Apple iOS and Google Android maintain more than 90 percent of the global smartphone marketshare.

IDC: Smartphone OS Market Share Chart

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The group also blasted companies with “online platforms” that allow them to become de facto gatekeepers, which encourages practices like biased search rankings and preferences for their own services or products.

As the writers note in the full letter:

"When working well, major online platforms – be they mobile operating systems, app stores, search engines, marketplaces or social media platforms – are gateways to the digital economy: They enable consumers to access innovative services, they spur innovation and help small businesses and start-ups reach new markets, and they drive investment, growth and employment.

"Notwithstanding, the very nature of online platforms – be it their sheer and growing scale and reach, the concentration of market power in a limited number of platforms, the tendency toward 'winner takes all' market dynamics and their already substantial and increasing impact on European citizens’ lives and across all aspects of the economy – requires careful consideration and response from policymakers."

The letter comes ahead of the European Commission’s upcoming May 10 review of the Digital Single Market, an EU initiative that focuses on consistent digital regulation and policy among EU members.

The CEO group said it hopes the commission will “to pursue a pro-growth, pro-consumer, balanced but targeted, legislative framework for online platform business-to-business (B2B) practices.” The commission is also expected to introduce new policies aimed at adjusting how Apple and Google can work with companies that rely on their app stores, Business Insider reported.

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In the past, Spotify has tussled with Apple over its App Store policies. Apple traditionally takes a 30 percent cut of in-app transactions — including subscription charges — and Spotify has argued the percentage is onerous to its bottom line. Recode reported Spotify also sent a letter to Apple last June arguing Apple’s rejection of a Spotify app update was “causing grave harm to Spotify and its customers” and alleged the company was favoring its own Apple Music service over competitors like Spotify.