Apple Inc. said its iPhones do not record audio without users' consent in a letter responding to U.S. lawmakers' questions about potential device privacy concerns.

In a letter to Greg Walden, R-Ore., chairman of the House Energy and Commerce Committee, the tech giant said iPhones only listen to users who speak specific audio commands after voice commands are enabled and microphone use is approved.

Apple also said it required third-party apps to clearly display if the microphone is in use and the app is listening.

Reuters first reported on the letter after viewing it Aug. 7. S&P Global Market Intelligence obtained a copy Aug. 8.

"The customer is not our product, and our business model does not depend on collecting vast amounts of personally identifiable information to enrich targeted profiles marketed to advertisers," Apple's director of government affairs said in the letter. "Customer privacy [is] a key element of design" for all of Apple's new products and services, he added.

A spokeswoman for the House Energy and Commerce Committee told Reuters that Apple and Alphabet Inc. "have been cooperative thus far." The committee in July requested both companies respond to its concerns related to third-party reports about potential privacy violations on iPhones and Android devices.