“Today’s big tech companies have too much power — too much power over our economy, our society, and our democracy,” the Massachusetts lawmaker wrote in a blog post published Friday on Medium.

The senator’s proposed legislation includes designating the tech giants as “platform utilities” and appointing regulators to break up mergers that harm market competition. She defines “platform utilities” as companies earning a global annual revenue of $25 billion or more and that “offer to the public an online marketplace, an exchange, or a platform for connecting third parties.”

According to Warren, breaking up the mergers will not only foster competition, it will also keep the pressure on tech giants to listen to user’s concerns, including about privacy.

The proposal would also bar companies from sharing user data with third parties.

Warren is the first of the 2020 Democratic presidential contenders to present a detailed policy to limit the power of tech corporations, although Senators Bernie Sanders (Vt.) and Amy Klobuchar (Minn.) have expressed similar ideas, the New York Times reports.

Amazon, Facebook, and Alphabet, which owns Google, all reported reported stock market losses after Warren’s announcement, as shares dropped as much as 1.5% on Friday, TIME reports.

Fortune has contacted the three tech companies for comment. Facebook declined comment

Warren’s proposal was released Friday ahead of a scheduled rally in Long Island City, New York. That’s the Queens neighborhood where Amazon recently canceled plans to build a second headquarters after facing community backlash from local residents and organizers.