A US House of Representatives committee is asking tech giants to turn over documents as part of a bipartisan probe of competition in the sector.
Members of the House Judiciary Committee have written to Amazon, Apple, Facebook and Google's parent company Alphabet requesting various internal documents.
They're looking for files including emails from senior executives responding to 'specific competition concerns'; documents from any government investigations (including outside the US) into the companies; and financial statements / reports for key products.
Senior members of the committee sent the letters to CEOs Jeff Bezos, Tim Cook, Mark Zuckerberg and Larry Page - asking for the documents by October 14th.
Ranking member Doug Collins said the Judiciary Committee is investigation "the relationship between big tech and market competition".
He observed: "The documents requested will provide the Committee with a better understanding of the degree to which these intermediaries enjoy market power, how they are using that market power, whether they are using their market power in ways that have harmed consumers and competition, and how Congress should respond.
"We made it clear when we launched this bipartisan investigation that we plan to get all the facts we need to diagnose the problems in the digital marketplace.
"Today’s document requests are an important milestone in this investigation as we work to obtain the information that our Members need to make this determination."
Tech giants are facing a number of probes and investigations in the US at the moment.
In July, it emerged the Department of Justice is conducting an anti-trust investigation into the companies over whether their online platforms have hurt competition.
It will examine how the major platforms have achieved market power and whether they 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.
