The Justice Department today filed a lawsuit against Apple, accusing it of violating antitrust laws by using its dominance in the smartphone market to undermine its competitors’ apps, devices and services. The suit claims that Apple’s practices have led to higher prices for customers and less innovation in the industry.

Sixteen states and the District of Columbia joined the lawsuit, which is the federal government’s most significant challenge to Apple’s reach.

The iPhone is Apple’s most popular product, and key to its growth into one of the world’s most valuable public companies. But critics say that by tightly controlling the user experience on iPhones and other devices, Apple has created an uneven playing field. It has limited finance companies’ access to the phone’s payment chip and Bluetooth trackers from tapping into its location-service feature. It’s also easier for users to connect Apple products, like smartwatches and laptops, to the iPhone than to those made by other manufacturers.

Apple says these practices make its devices more secure than other smartphones, but rivals argue that Apple has built itself up by crushing competition.

Today’s lawsuit is the latest in a series of regulatory actions that are hitting the tech giant. Here are the other challenges.