The European Union opened what it called an in-depth investigation into Apple’s proposed acquisition of London-based music identification service Shazam, E.U. regulators announced Monday. Regulators are concerned the acquisition could reduce choice for music streaming services, they said in a press release.

“The way people listen to music has changed significantly in recent years, with more and more Europeans using music streaming services,” E.U. commissioner Margrethe Vestager said.”Our investigation aims to ensure that music fans will continue to enjoy attractive music streaming offers and won’t face less choice as a result of this proposed merger.”

Apple officially announced the acquisition of Shazam in December. The company didn’t reveal a purchase price at the time, but the deal is reportedly worth $400 million. Apple didn’t immediately respond to a request for comment Monday morning.

Shazam is best known for its music recognition apps, which have been downloaded more than 1 billion times across a variety of mobile platforms. Apple hasn’t detailed its plans for the company, but said in a statement in December that the two were “a natural fit, sharing a passion for music discovery and delivering great music experiences to our users.”

On Monday, the European Commission said it was concerned about what this pairing up would mean for others in the market. “The Commission is concerned that, following the takeover of Shazam, Apple would obtain access to commercially sensitive data about customers of its competitors for the provision of music streaming services,” it said. “Access to such data could allow Apple to directly target its competitors’ customers and encourage them to switch to Apple Music.”

Regulators said they would also investigate whether competing streaming music services would be harmed if Shazam were to stop sending them any referral traffic. Shazam used be a significant source of referral traffic for music downloads, with executives at one point claiming that users of its app bought 500,000 songs a day. The app’s impact on streaming services is unknown.

The European Commission plans to conclude its investigation by Sept. 4.