Big tech just got put on notice.

The Justice Department said Tuesday that it would review online platforms – supposedly including social networks such as Facebook and Twitter, and likely tech giants Google and Amazon – for potential anti-competitive and anti-consumer actions.

The Department's Antitrust Division will be examining whether online platforms have gained their powerful market positions by "engaging in practices that have reduced competition, stifled innovation, or otherwise harmed consumers," the agency said in an announcement.

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

The review will look into concerns "about search, social media, and some retail services online" from consumers, businesses and entrepreneurs, the DOJ says.

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This review comes as a growing number of lawmakers have called for stricter regulation or even breaking up of the big tech companies, which have come under intense scrutiny after a series of scandals that compromised users' privacy.

The Justice Department had already been reportedly preparing an antitrust investigation of Google's internal practices and search rankings, according to a report published late last week. And Facebook is facing a $5 billion fine from the Federal Trade Commission as the result of an investigation into its privacy practices, according to reports.

"What seems clear is that DOJ is opening a probe because it is concerned about the lack of competition," said Carl Tobias, a professor at the University of Richmond (Va.) School of Law. "It remains unclear if DOJ is working with the FTC and other agencies and with Congress and where the probe might lead. Big tech should be concerned that an official probe has been opened."

President Trump also has recently criticized the big tech companies by name in recent months, and railed against what he called a "terrible bias" against conservatives on social media.

Amazon, Facebook and Google did not immediately respond to requests for comment from USA TODAY. Twitter declined to comment.

Apple referred to CEO Tim Cook's comments last month to CBS News' Norah O'Donnell, when he said: "I think that with size, I think scrutiny is fair. I think we should be scrutinized. 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. Our share is much more modest. We don't have a dominant position in any market."

Similarly, Google pointed to statements Adam Cohen, Google’s director of economic policy, made at a U.S. House hearing last week. "We have helped reduce prices and expand choice for consumers and merchants in the U.S. and around the world," he said. "We have created new competition in many sectors, and new competitive pressures often lead to concerns from rivals. We have consistently shown how our business is designed and operated to benefit our customers."

The Associated Press contributed to this report.