Google’s and Apple’s large cut of app-store and in-app purchases has become a hot legal topic of late, particularly since Epic Games sued both mobile-ecosystem giants over the issue nearly a year ago. State attorneys general have sued Google in the U.S. over the allegedly monopolistic practice, EU antitrust regulators have charged Apple, and regulators have launched probes in South Korea (regarding Google) and in the U.K. (regarding Apple).

Now comes the U.K. collective action, which is being fronted by “consumer champion” Liz Coll, a former consumer policy lead at the charitable organization Citizens Advice. Coll and the lawyers assisting the suit, Hausfeld & Co., say they are acting on behalf of around 19.5 million people in the U.K. who have bought apps or in-app digital content, services, or subscriptions since Oct. 1, 2015.

“Google created the Android app marketplace, and controls it with a vice-like grip,” Coll said in a Thursday statement. “Customers are herded towards the Google Play store, and once there have no option but to pay a 30% fee whenever they buy an app or make an in-app purchase. Competing app stores, which could give the same service at a fraction of the price, never get a look in.

“Google is a gatekeeper to so many digital services, and it has a responsibility not to abuse that position and overcharge ordinary consumers. These hidden charges are unlawful, and Google’s customers deserve compensation, and better treatment from Google in future.”

The suit does not cover app-based purchases of physical goods and services like Uber and Deliveroo—which don’t incur Google’s commission—nor does it cover purchases made within Google’s own apps.

Google had not replied to a request for comment at the time of publication.

Hausfeld also led a similar suit in May, targeting Apple for the same practices, on behalf of up to 19.6 million U.K. users—Android and iOS each hold about half the U.K. mobile market. On that occasion, the suit was filed by Rachael Kent, a digital-economy professor at King’s College London.

This is not the first time Google has been hit with a collective legal action in the U.K., though the last suit was about privacy rather than antitrust.

In 2017, another consumer champion named Richard Lloyd—a veteran activist who is now on the board of the Financial Conduct Authority—sued Google on behalf of iPhone users whose browsing information had been scooped up by Google in a circumvention of Safari’s tracking protections.

However, that suit foundered at the High Court the following year, because the judge said Google’s privacy-busting behavior didn’t actually damage consumers, even though it was arguably “wrongful and a breach of duty.”