Shares of leading tech giants slid Monday on reports that antitrust regulators are taking steps that could lead to greater oversight.

Shares of Amazon fell more than 4 percent Monday following a Washington Post report that the top U.S. antitrust enforcement agencies have a new agreement over tech oversight. The drop shaved about $35 billion from its market cap, bringing it to $839 billion.

Shares of Facebook were down Monday morning, but slid even further after The Wall Street Journal reported that the FTC will be able to examine the effect of Facebook’s practices on digital competition.

Facebook shares hit session low, down more than 6.6%, after reports say the FTC will examine Facebook's business practices https://t.co/LFPn1pitDK pic.twitter.com/qoMTlhsReU — CNBC Now (@CNBCnow) June 3, 2019

The stock closed the day down 7.5 percent following the report, shaving more than $33 billion from its market cap and bringing it to about $472 billion.

Facebook is already under investigation by the FTC over its handling of user data and has said it is expecting a fine of up to $5 billion.

Shares of Google parent company Alphabet finished the day down more than 6 percent after The Wall Street Journal reported the Justice Department is readying an antitrust investigation. The stock lost about $47 billion from its market cap, bringing it to around $721 billion.

Apple also declined on Monday after Reuters reported the Justice Department has been given jurisdiction to probe the company’s practices as part of a broad review into potential anti-competitive behavior among big tech companies.

The stock dropped about 1 percent following the report, after trading higher earlier in the day. Apple and CEO Tim Cook are presenting updates to the company’s central software at the annual Worldwide Developers Conference.

Antitrust regulation has remained a distant threat in recent years as scandals like Cambridge Analytica brought the scale of tech power into focus for the public. In the lead up to the 2020 presidential election, “break up big tech” has become a rallying cry for some, Democratic presidential candidate Sen. Elizabeth Warren, D-Mass.

But a new reported agreement between the Federal Trade Commission and the Department of Justice brings that threat a bit closer to reality. The FTC will take the lead on oversight of Amazon, which the DOJ will have greater jurisdiction over Google, according to the Post.

The FTC previously closed an investigation of Google without taking action, but now the DOJ will take another look into Google’s practices in search and other areas, according to the Journal.