The Department of Justice is launching an antitrust probe into some of the world's biggest and most influential tech companies, the agency announced Tuesday.

The department's Antitrust Division, which is responsible for reviewing and enforcing issues relating to mergers, monopolies, competition, and price-fixing, said its review would "consider the widespread concerns that consumers, businesses, and entrepreneurs have expressed about search, social media, and some retail services online."

“Without the discipline of meaningful market-based competition, digital platforms may act in ways that are not responsive to consumer demands,” Makan Delrahim, head of the Antitrust Division, said. “The Department’s antitrust review will explore these important issues.”

The DOJ didn't name any names, but the list of "market-leading online platforms" accused of stifling competition through dishonest tactics, or simply of being too big for competitors to exist against, generally has Amazon, Facebook, and Google at the top; all three companies' stocks immediately tanked following the announcement.

Reports by several media outlets earlier this year, citing the ever-popular "sources familiar with the matter," indicated the DOJ and Federal Trade Commission were planning something of a divide-and-conquer approach to tech sector regulation, with the DOJ digging into Apple and Google, and the FTC handling Amazon and Facebook.

Widespread scrutiny

The Justice Department is just the latest, not the first, body to take a hard look at what the tech sector has gotten up to in the past decade.

Congress kicked off its own probe into big tech's behavior last month, when the House Antitrust Subcommittee launched a bipartisan investigation into "competition in digital markets." The subcommittee chair, Rep. David Cicilline (D-R.I.) at the time called the growth of monopolies in the US economy "one of the most pressing economic and political challenges we face today."

Massachusetts Senator Elizabeth Warren, a Democrat who is one of the party's leading candidates in the 2020 presidential primary race, in March issued a call to use existing antitrust law to break up Amazon, Google, and Facebook.

Traditional bricks-and-mortar retailers have also been asking regulators to update antitrust policy in order to rein in Google and Amazon, which dominate the online marketplace through what the retailers say are anticompetitive practices.

The DOJ is also lagging behind its international peers. Germany, Austria, Italy, and the European Union have all launched separate antitrust investigations into Amazon's behavior with third-party merchants on its marketplace since November, and the EU has fined Google billions of dollars four separate times in recent years for violations of European monopoly law.