Sens. Richard Blumenthal (D-Conn.), Amy Klobuchar (D-Minn.) and Marsha Blackburn (R-Tenn.) on Wednesday introduced legislation intended to promote competition among app stores.

The bipartisan Open App Markets Act takes aim at Google's and Apple’s dominant app stores, which the lawmakers say use their gatekeeping power to stifle potential rivals.

“For years, Apple and Google have squashed competitors and kept consumers in the dark—pocketing hefty windfalls while acting as supposedly benevolent gatekeepers of this multi-billion dollar market,” Blumenthal said in a statement. “This bipartisan bill will help break these tech giants’ ironclad grip, open the app economy to new competitors, and give mobile users more control over their own devices.”

The Senate Judiciary antitrust subcommittee held a hearing on app stores earlier this year that featured companies criticizing the two big markets for imposing excessive commission fees on payments and threatening up-and-coming developers.

The Open App Markets bill would try to remedy those concerns by blocking Apple and Google from requiring developers to use their payment systems or taking punitive action against developers that sell their services at lower prices elsewhere.

The legislation would also enshrine the right of users to download apps from third-party stores, called sideloading, and stop the dominant app stores from “unreasonably” promoting products made by them.

The bill has been endorsed by a wide variety of consumer rights, digital access and anti-monopoly groups.

It has also drawn support from apps that have struggled to operate through the major app stores.

“Ending these monopoly abuses on mobile payments would not only create fairer prices, but also promote competition while benefiting developers and consumers alike,” Andy Yen, CEO of the encrypted mail service Proton, said in a statement.