The activism from smaller rivals adds to scrutiny the tech giants are facing from U.S. and European regulators and lawmakers.
Apple is the group's main target, though Google's app store policies are also on its radar.
Both companies this summer dropped the popular game Fortnite from their app stores after the game’s developer introduced a direct payment plan that bypasses their platforms.
Apple and Google both take a 30% cut from in-app revenue purchases, which has long been a sore spot with developers.
Epic is backing the new coalition along with Spotify, online dating app maker Match Group, and other members including Tile, Basecamp, ProtonMail and European media industry associations.