Federal regulators may be inching closer to probing the market dominance of some of the largest technology companies. The Federal Trade Commission and Department of Justice are said to have divided up oversight of Facebook\n \n (FB), Google\n \n (GOOGL), Apple\n \n (AAPL) and Amazon\n \n (AMZN), paving the way for potential investigations into antitrust violations. On Monday, multiple outlets, citing sources, reported that the FTC would assume responsibility for any antitrust investigation into Facebook. The agency has been investigating Facebook for more than a year after the Cambridge Analytica scandal raised the prospect that Facebook had violated a 2011 consent agreement with the agency. The FTC is expected to levy a record multi-billion dollar fine against the social media company. Meanwhile, the Justice Department is laying the foundation for a potential antitrust investigation of Google, three people familiar with the matter told CNN over the weekend. Multiple sources said the DOJ may focus on Google’s search business. The FTC is also reportedly gaining greater oversight of Amazon and the Department of Justice is said to have the right to probe Apple. The FTC declined to comment. Google and Amazon declined to comment. Representatives for Apple and Facebook did not immediately respond to a request for comment. While these early moves may send a signal that tech giants are being closely scrutinized, there’s no guarantee the agencies will ultimately open antitrust investigations into any or all of these companies. The news rattled Wall Street. The four tech companies lost tens of billions of dollars in market value Monday as investors digested the heightened risk of antitrust probes. Google and Facebook were hardest hit, with their stocks tumbling as much as 7% and 9%, respectively. Once hailed by politicians like former President Barack Obama as representing the best of American innovation, big tech companies have found themselves contending with mounting antitrust scrutiny from state officials, federal regulators and the European Union. Rep. David Cicilline, the chairman of the House Antitrust Subcommittee, has called for an antitrust investigation into Facebook, with a focus on its acquisitions of Instagram and WhatsApp, both of which now have more than a billion users. The EU has hit Google with three separate billion-dollar antitrust fines, the most recent of which was in March for abusing its dominant position in online search advertising. And the US Supreme Court ruled this month that iPhone owners can sue Apple for monopolizing the App Store. Sen. Elizabeth Warren, a Democratic presidential candidate, put out an aggressive plan in March to break up Facebook, Google and Amazon, the latter by unwinding its acquisitions of Whole Foods and online shoe retailer Zappos. Sen. Kamala Harris, another Democratic presidential candidate, said this month that “we have to seriously take a look” at breaking up Facebook, which she argued had “prioritized its growth over the best interests of its consumers.” So far, there have been mixed reactions to reports of heightened federal antitrust scrutiny from Democrats in Congress who have pressed for greater checks on the tech industry’s power. Sen. Richard Blumenthal, a Democrat representing Connecticut, said “stiff DOJ scrutiny is overdue.” Rep. Cicilline said in a statement Saturday that he did not “have a lot of faith that President Trump’s Justice Department will stand up for working people against powerful corporations like Google and Facebook.” Some in Silicon Valley have been prepping for an antitrust showdown. Facebook and Amazon have staffed up with former antitrust lawyers from the Department of Justice. A number of the companies have also been racing to prove they are putting their customers’ privacy first.