Apple Inc. was hit with an antitrust lawsuit over Apple Pay—accused of, first, using its market power in the mobile device industry to fend off competition from rival payment apps and, second, charging card issuers fees to boost its bottom line.

The proposed class-action complaint by Affinity Credit Union marks the latest antitrust battle for the iPhone maker, after it's faced increasing regulatory scrutiny in recent years over its App Store policies. European regulators, after a nearly two-year investigation, also found on a preliminary basis that Apple abused its dominant position with Apple Pay in the market for tap-to-pay apps or mobile wallets.