Apple has defended the fees it charges developers to sell their digital products via its App Store.
The iPhone-maker says a study it commissioned shows content makers give away a similar cut to dozens of other online markets, and an even bigger share if their goods are sold offline.
Apple is facing complaints about the matter on both sides of the Atlantic.
The EU launched a competition probe in June, and chief executive Tim Cook will give testimony to Congress on Monday.
He will appear before the House Judiciary Antitrust Subcommittee alongside counterparts from Amazon, Facebook and Google. The tech giants all face claims that they have abused their market-leading positions.
It has emerged that ahead of the hearing, Microsoft's president briefed the panel that his firm had concerns about the way Apple operated the App Store.
According to a report in the Information, Brad Smith has drawn attention to issues including::
-apps cannot easily be installed onto iOS devices by other means
-moderators' decisions about whether to approve or reject apps sometimes seem arbitrary
-developers must share a cut of in-app fees, and cannot promote alternative ways to pay within their products