The US Department of Justice has expanded its antitrust investigation into Apple after the Android messaging app Beeper Mini was shut down, the New York Times reported.
Beeper Mini allows Android users to send messages to iPhone without creating an Apple account.
Messages sent from the Beeper Mini appear in the iMessage chat app built into the recipient's iPhone.
Apple blocked the app by making technical changes to iMessage three days after its release.
Beeper temporarily restored the service, but decided to shut it down shortly afterwards, saying: "We can't win this cat-and-mouse game with the biggest company in the world."
This development caught the attention of the Ministry of Justice.
Four years ago, the government launched an antitrust investigation into Apple. The Wall Street Journal said in February that the investigation aims to determine whether the iPhone maker gave its apps an unfair advantage over competitors.
The Justice Department is investigating other aspects of the company's interactions with third-party developers.
Beeper founder Eric Migicowski met with a Justice Department antitrust lawyer on December 12.
Days later, a bipartisan group of lawmakers called on the administration to investigate whether Apple violated competition laws by banning the app.
In statements calling for an investigation, lawmakers said interoperability was a key factor in the competition.
Apple said it shut down the Beeper Mini app because it posed a cyber risk. The iPhone maker claims that the Beeper Mini allows Android users to send messages to iMessage using technology that exploits fake credentials.
The company says the app increases the risk of user metadata leaks, spam, and phishing attacks.
In a sign that the US Federal Trade Commission may also be looking into the matter, the agency appears to address the controversy surrounding the Beeper Mini in a recent blog post.
“Given concerns about anti-competitive behavior, companies cited privacy and security as reasons to refuse to interact with their products and services,” the blog says.
“As an agency that enforces competition and consumer protection laws, the agency is uniquely positioned to evaluate competitive privacy and security claims,” the FTC added.
The fact that iMessage does not interact with third-party chat services has become an issue for politicians in the European Union.
European lawmakers passed an antitrust law called the Digital Services Act last year.
The law includes a provision that says dominant messaging platforms must allow users to send messages to competing services like Beeper Mini if the developers of those services need interoperability.
Apple has argued that interoperability requirements should not apply to iMessage, though the company is taking steps to address regulators' concerns.
In November last year, Apple announced plans to make iPhones compatible with the RCS messaging protocol next year.
This compatibility allows iPhone and Android users to exchange messages, though it's unclear whether Apple plans to add the messaging protocol to iMessage or implement compatibility differently.