The Coalition for App Fairness, a group of developers targeting what they claim is Apple’s unfair control of the App Store, has more than doubled in size since its formation last month.

According to a new report, the original group of 13 companies — which included the likes of Epic Games and Spotify — has now increased to 40, with another 400 requests to join.

Spotify, Match, and Fortnite developer Epic Games have joined a nonprofit that advocates for regulatory and legal action against Apple for what they claim is it unfair control of the App Store.

Their main objection is the way that Apple charges up to 30 percent for in-app payments. Apple lays out a detailed set of rules which apps must follow in order to be allowed in the App Store.