Letters addressed to Facebook CEO Mark Zuckerberg, Alphabet CEO Larry Page, Amazon CEO Jeff Bezos and Apple CEO Tim Cook were sent out Friday 

House has requested internal emails between top stakeholders related to the companies' biggest competitors and companies they have acquired

Subcommittee on Antitrust, Commercial, and Administrative Law's Chairman David N. Cicilline it marked an 'important milestone in this investigation'

Democrat Cicilline called it an 'opportunity for tech giants to ensure that the Internet is an engine for opportunity for everyone, not just a select few' 

Chairman Jerry Nadler said there's 'evidence that a handful of corporations have come to capture an outsized share of online commerce and communications' 

House lawmakers launched their investigation in June calling the Web 'broken' 

The Judiciary Committee grilled officials from the companies at a hearing in July