Apple Music is subject to antitrust investigations
Apple Music is currently facing three antitrust investigations in Europe and the USGetty Images

A US senator is complaining about high prices charged by Apple on its in-app subscription services, calling on regulators to probe the company for possible antitrust violations in the music streaming market.

In a letter sent to the US Justice Department and the Federal Trade Commission (FTC), senator Al Franken said the regulators need to ensure meaningful competition in the ever-evolving digital music industry.

"While I am encouraged to see increased competition in this market, I am concerned about certain business practices that have the potential to limit choices and raise prices for consumers," the Minnesota Democrat writes.

"Apple's position as a dominant platform operator may actually undermine many of the potential consumer benefits of its entry into the market. To protect consumer choice and promote greater transparency of pricing, I ask that you review Apple's business practices with respect to its competitors in the music streaming market."

Along with its recent launch of Apple Music, the iPhone maker has put in place a number of restrictions on app developers, including its own competitors that use the iOS platform.

While Apple charges a 30% fee on revenues from in-app purchases, it restricts app developers from communicating important information to their users, such as lower prices available through their own websites. In addition, Apple restricts developers from advertising the availability of discounts and completing a transaction directly with a customer.

"These types of restrictions seem to offer no competitive benefit and may actually undermine the competitive process, to the detriment of consumers, who may end up paying substantially more than the current market price point," Franken says.

Apple's rival Spotify earlier urged customers to sign up for its service through its own website, rather than through the Apple App Store. While Spotify charges $9.99 (£6.40, €9.14) per month for its standard streaming service, customers availing the service via App Store have to pay $12.99.

Tech news site the Verge earlier reported that the FTC has launched an investigation into Apple's dealings with competing music streaming services in its App Store. The regulator has already issued subpoenas to music streaming services, according to the report.