The federal government has turned its full investigative powers toward examining the world's biggest technology companies, building on a growing backlash against the industry.

The Justice Department said Tuesday that it would start an antitrust review into how internet giants had accumulated market power and whether they had acted to reduce competition. Similar inquiries are underway in Congress and at the Federal Trade Commission, which shares antitrust oversight responsibilities with the Justice Department.

The action is the clearest sign yet that the longtime arguments that helped shield the tech giants from antitrust scrutiny are eroding. Since the 1970s, a consensus in antitrust circles has been that if companies were focused on consumer welfare — for example, by offering low prices — they were not likely to attract federal intervention.

Since companies like Google and Facebook largely provide free services, the thinking went, they were not subject to federal antitrust examination.

But that approach has evolved, pushed by scholars and others, as concerns about the clout and reach of Google, Facebook, Amazon and Apple have grown. The Justice Department has recently been meeting with tech industry experts to learn what kinds of harm the companies may have caused, said two people with knowledge of the talks, who spoke on the condition of anonymity.

"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 Justice Department's antitrust division, said in a statement. "The department's antitrust review will explore these important issues."

Attorney General William Barr himself has plunged into the conversation about tech power. On Tuesday, he said in a speech in Manhattan that tech companies should stop using advanced encryption and other security measures that effectively turn devices into "law-free zones," essentially criticizing Apple and its iPhones without naming them.

In announcing its review, the Justice Department did not name specific companies, but said it would look into concerns about search, social media and some retail services — presumably putting Google, Facebook and Amazon on notice.

The Justice Department declined to comment beyond its announcement; Google and Facebook also declined to comment. Amazon did not immediately respond to a request for comment. Apple referred to comments made by Tim Cook, its chief executive, in a recent television interview with CBS News.

"I think we should be scrutinized," Cook said at the time. "But if you look at any kind of measure about 'is Apple a monopoly or not,' I don't think anybody reasonable is going to come to the conclusion that Apple's a monopoly."

The Justice Department's review may not lead to full-blown investigations of the companies. But the timing of the announcement ratchets up pressure on the tech giants. Across Washington in recent weeks, lawmakers and regulators have united to raise questions about Facebook, Google, Amazon and Apple.

This month, the FTC voted to fine Facebook about $5 billion for mishandling users' personal information, by far the agency's largest fine against a tech company. An official announcement of a settlement is expected as soon as Wednesday.

Last week, Facebook faced lawmakers over two days of grilling for a new cryptocurrency initiative called Libra. Google was at the center of a Senate subcommittee hearing about censorship in searches. And at a separate House hearing, with witnesses from Google, Facebook, Amazon and Apple, Rep. David Cicilline, D-R.I., who leads a subcommittee on antitrust law, said that the government stance for too long was to celebrate the new tech economy rather than scrutinize its corporate leaders.

"Congress and antitrust enforcers allowed these firms to regulate themselves with little oversight," Cicilline said. "As a result, the internet has become increasingly concentrated, less open and growingly hostile to innovation and entrepreneurship."