Britain’s competition regulator said on Thursday it has opened an investigation into Apple Inc after complaints that the iPhone maker’s terms and conditions for app developers are unfair and anti-competitive.

The Competition and Markets Authority (CMA) said the investigation would look into whether Apple has a monopoly in the sale of software on its devices in the UK.

Apple’s App Store payment practices have long been a source of contention among app developers. It charges developers a fee of up to 30% of the purchase value or every time a buyer buys their app.

Apple has confirmed that it would cooperate with the regulator.

In a statement, Apple said, “The App Store has been a driver of success for app developers, in part because of the strict standards we have in place — applied fairly and equally to all developers — to protect users from malware and prevent rampant data collection without their permission.”

The firm is also being investigated by the Dutch antitrust authorities on similar grounds, and a draft decision is expected soon.

Last year, the European Commission launched its own investigation into Apple’s App Store commission fee.

“Complaints that Apple is using its market position to set terms which are unfair or may restrict competition and choice – potentially causing customers to lose out when buying and using apps – warrant careful scrutiny,” CMA Chief Executive Andrea Coscelli said.