The US government's investigation into big tech was expanded on Friday when lawmakers announced they would request internal documents from Google, Facebook, Amazon, and Apple.

On Friday, the four companies received letters from the heads of the House Judiciary Committee and its Subcommittee on Antitrust, which conducted a full antitrust investigation of companies and their impact on competition and consumers.

Among the dozens of executives named in the questions are Amazon founder Jeff Bezos, Apple CEO Tim Cook, Facebook co-founder Mark Zuckerberg and Google's Larry Page, Sergey Brin and Eric Schmidt.

Chair of the committee, Jerrold Nadler, a Democrat, said: "The open internet has brought tremendous benefits to Americans, including a flood of economic opportunities, massive investment and new ways to educate online.

"However, there are increasing signs that a handful of companies have come to conquer an overwhelming share of online commerce and communication."

The investigation is a rare example of bipartisan cooperation.

Doug Collins, Republican High Representative on the House Committee, said, "This information is critical to determining whether anticompetitive behavior exists, whether our antitrust authorities should investigate certain issues, and whether our antitrust laws need to be improved to better promote European competition the digital markets. "

The investigation is likely to lead to the publication of potentially embarrassing internal documents and high-level public hearings involving some of the biggest names in the tech industry.

The letters look for information on how technology giants have built their business, how they shape consumer search results, and how other companies interact with their services.

Companies have announced their full participation in the Congressional investigation.

The legislature has set a deadline of 14 October for the companies to submit the documents.

Nadler said the documents would help the committee understand "whether they use their market power in a way that has harmed consumers and the competition."

The Department of Justice and the Federal Trade Commission (FTC) are also investigating the companies. The latest moves came after dozens of US states launched data protection and antitrust investigations on Facebook and Google.

Associated Press contributed to this report