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A panel of U.S. senators questioned officials from Apple Inc (AAPL.O) and Alphabet Inc’s (GOOGL.O) Google on Wednesday about the dominance of their mobile app stores and whether the companies abuse their power at the expense of smaller competitors.

Amy Klobuchar, the top Senate Democrat on antitrust issues, said Apple and Google can use their power to "exclude or suppress apps that compete with their own products" and "charge excessive fees that affect competition."

App makers like music streaming service Spotify Technology SA (SPOT.N) and dating services giant Match Group (MTCH.O), which owns the Tinder app, have long complained that mandatory revenue sharing for sales of digital goods and strict inclusion rules set by Apple's App Store for iPhones and iPads, along with Google's Play store for Android devices, amount to anticompetitive behavior.

Representatives for Apple and Google told senators that the companies' tight control over their stores and the associated revenue-sharing requirements are needed to enforce and pay for security measures to protect consumers from harmful apps and practices.