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Lawmakers on Capitol Hill sent letters to Facebook, Amazon, Google and Apple on Friday requesting a trove of documents and other information as part of an antitrust investigation into online markets.

Leaders of the House Judiciary Committee sent detailed requests asking for general information on the companies and their competitors in online commerce and content, as well as executive communications related to acquisitions and other competition matters. The companies were also asked to turn over any documents from prior investigations by US or foreign regulators in the past 10 years. The House committee said documents should be turned over by Oct. 14.

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The probe was announced in June by Rep. David N. Cicilline, a Democrat from Rhode Island and chairman of the House antitrust subcommittee. The investigation is exploring competition in online markets and whether big tech companies are engaging in "anti-competitive conduct." It'll also try to decide if the government's current antitrust laws and enforcement policies are enough to fix the problems.

The House probe comes as tech giants faces a flood of scrutiny from government regulators, who've targeted tech companies over potential anti-competitive behavior, privacy breaches and data misuse. The Department of Justice and Federal Trade Commission, the two US agencies that handle antitrust issues, are looking into tech companies' business practices. Fifty state attorneys general earlier this week opened antitrust investigation into Google, and last week, New York Attorney General Letitia James announced a similar probe into Facebook.

Amazon declined to comment. Apple and Facebook didn't immediately respond to a request for comment.

Google pointed to a blog post it published last week written by Kent Walker, senior vice president of global affairs. In the post, Google acknowledges the regulatory scrutiny and said it'll work with government officials.