An additional four states joined a lawsuit levelled at Apple by the US Department of Justice in March which accuses the iPhone-maker of anti-competitive conduct in the smartphone ecosystem.

In a filing, legal representatives from Indiana, Massachusetts, Nevada and Washington claimed Apple’s practices have hurt multiple smartphone-related markets and sectors beyond the devices segment, throwing weight behind the lawsuit originally filed by 15 states and the District of Columbia.

The four new additions argued Apple’s “shapeshifting rules and restrictions” in its App Store allow the company to “extract higher fees, thwart innovation, offer a less secure or degraded user experience and throttle competitive alternatives”.

This business model, they argue, is also deployed for other products and services including smartwatches and mobile wallets.

Apple is accused of deploying its in-app payment mechanism to “lock in” both developers and users, and impose restrictions designed to complicate the ways they can leave the platform.

This hinders developers’ ability to negotiate high commission fees through alternative app stores and in-app payment systems, the accusers claim, noting Apple also charged banks substantial fees for every “tap-to-pay transaction” on its iPhone.

“Apple’s anticompetitive conduct not only limits competition in the smartphone market, but also reverberates through the industries that are affected by these restrictions, including financial services, fitness, gaming, social media, news media, entertainment, and more”, the statement read.

The legal representatives also raised concerns about Apple’s growing influence in the automotive and financial industries given its alleged activities.

“Unless Apple’s anticompetitive and exclusionary conduct is stopped, it will likely extend and entrench its iPhone monopoly to other markets and parts of the economy,” it added.