WASHINGTON — The federal government is stepping up its scrutiny of the world’s biggest tech companies, as regulators divvy up oversight of the Silicon Valley giants and lawmakers move to investigate whether they have stifled competition.
After recent negotiations, the Justice Department will handle Apple and Google, while the Federal Trade Commission will take Facebook and Amazon.
Lawmakers in the House said on Monday that they were looking into concerns that could lead to the first overhaul of antitrust rules in decades, in a push to keep pace with a rapidly changing industry.
The focus on antitrust, long relegated to academic debates and industry griping, has now entered the political world, leaving the tech giants potentially vulnerable to new regulations and federal lawsuits.
Silicon Valley has faced fierce criticism in recent years over disinformation, privacy breaches and the misuse of data. President Trump regularly criticizes the power of the companies, as do several Democrats running for president.
The prospect of action pummeled technology stocks on Monday. Shares of Facebook fell more than 7 percent on Monday afternoon. Google and Amazon shares were also sharply lower. Apple’s stock fell about 1 percent.
Lawmakers and regulators have long struggled to keep pace with technology companies, which dominate large portions of the economy. But concerns about the businesses have been building, most notably since the 2016 presidential election.
Facebook and Google have attracted scrutiny for how they handle user data, and for perceived political bias on their platforms. Apple wields tremendous influence over software developers and what can appear on its devices. And Amazon, by far the leading online retailer, is often accused of stifling competition.
The moves from regulators and lawmakers are preliminary. But they will almost certainly lead to years of headaches for the companies. They also raise the prospect of aggressive actions in the future, like a lawsuit to break up a company, or a law limiting the reach of the companies.
“This is about how do we get competition back in this space,” Representative David Cicilline, Democrat of Rhode Island, said Monday in a news conference. Mr. Cicilline is the chairman of the House Judiciary’s subcommittee on antitrust, which will conduct the investigation.
He said the investigation would focus on major digital platforms. The House committee on Monday informed four tech companies, Google, Apple, Facebook and Amazon, of the plans, Mr. Cicilline said.
“This is long overdue,” he said.
The F.T.C. and Justice Department declined to comment Monday. All four companies have also declined to comment.