The US Department of Justice is opening an anti-trust investigation into big technology companies over whether their online platforms have hurt competition.
It will examine how market-leading online platforms have achieved market power and are engaging in practices that have reduced competition, stifled innovation or otherwise harmed consumers.
The department says its review will also consider "widespread concerns" about search, social media, and some retail services online.
It adds that these concerns were brought to light by consumers, businesses and entrepreneurs.
It is also consulting with and seeking information from the public - including industry participants who have direct insight into competition in online platforms - as well as others.
US Assistant Attorney-General Makan Delrahim is from the US Justice Department antitrust division.
He says: "Without the discipline of meaningful market-based competition, digital platforms may act in ways that are not responsive to consumer demands.
"The department's antitrust review will explore these important issues."
It says that the goal is to assess the competitive conditions in the online marketplace "in an objective and fair-minded manner".
It also wants to ensure people have access to free markets in which companies compete on the merits to provide services that users want.
"If violations of law are identified, the department will proceed appropriately to seek redress", it adds.
No companies were explicitly named in the announcement - but it is understood Apple, Amazon, Facebook and Google are likely to be examined.
It comes just a week after the European Commission opened its own formal investigation into possible anti-competitive behaviour of online retailer, Amazon.
It relates to whether Amazon's use of sensitive data, from independent retailers who sell on its marketplace, is in breach of EU competition rules.
It is looking into standard agreements between Amazon and marketplace sellers - in particular, focusing on whether and how the use of accumulated marketplace seller data by Amazon as a retailer affects competition.
It is also examining the role of data in the selection of the winners of the 'Buy Box', which is displayed prominently on Amazon and allows customers to add items from a specific retailer directly into their shopping carts.