Critics say fees charged by Google and Apple at their mobile app stores are excessive and cost developers collectively billions of dollars a year, a sign of the two companies' monopoly power.
Questionnaires were sent to developers last month, the people said.
Of the 16 questions in the document, some covered the period 2017-2021 and others 2019-2021. The European Commission declined to comment. Google did not respond to an emailed request for comment.
The U.S. tech giant has said apps would be removed from its app store starting June this year if developers do not use its billing system.
Respondents were asked whether Google's policy change this year impacted the distribution of their goods or services on Google Play Store, which apps were affected and if it affected their ability to acquire users on Android devices, the people said.
Regulators wanted to know if the change has forced developers to drop other payment options in favour of Google Billing and whether migrating users to another payment option affected the number of pre-existing users and the developers' access to data.
Developers were asked whether they believed they could offer a better service or product if they have the option of another payment system.
The EU competition enforcer also wanted to know if Google allowed them to use an alternative payment system, charged a service fee for this or complained about the security of their payment method.
App developers were asked if U.S. payments giant Stripes, Dutch payment system Adyen and PayPal unit Braintree are seen as alternative payment systems.
Last month, Google said non-gaming app developers can switch to rival payment systems with a lower fee of 12% instead of 15%, with the move applying to European users, in order to comply with EU rules that will come into force next year.
Politico first reported about the Commission's query.
(Reporting by Foo Yun Chee; Editing by Kirsten Donovan)
By Foo Yun Chee