WASHINGTON—U.S. antitrust enforcers have begun looking at the terms Apple Inc. set this week for media companies who want to sell their content on its popular iPad and other devices, according to people familiar with the matter.

The Justice Department and Federal Trade Commission's interest in Apple's new subscription service is at a preliminary stage, and might not develop into either a formal investigation or any action against the company. But it comes as Apple has attracted growing antitrust scrutiny in the U.S. and Europe.

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