Lawmakers leading a bipartisan big tech antitrust investigation are demanding documents — including the communications of top executives — from Apple, Amazon, Facebook and Alphabet’s Google.

On Friday, the House Judiciary Committee announced it sent requests to the tech companies asking for information about a sweeping range of topics — including their market share, competition and acquisitions.

Rep. David Cicilline (D-RI), who leads the antitrust subcommittee, called the document request an “important milestone.”

“We expect stakeholders to use this opportunity to provide information to the Committee to ensure that the Internet is an engine for opportunity for everyone, not just a select few gatekeepers,” said Cicilline in a statement.

House Judiciary Chairman Jerry Nadler (D-NY) said the documents will give the committee a better idea of how the tech giants are using their market power and how Congress should respond.

“The open Internet has delivered enormous benefits to Americans, including a surge of economic opportunity, massive investment, and new pathways for education online. But there is growing evidence that a handful of corporations have come to capture an outsized share of online commerce and communications,” Nadler said.

Republicans on the committee have stressed the importance of keeping an open mind, until investigators reach a conclusion.

“This information is key in helping determine whether anticompetitive behavior is occurring, whether our antitrust enforcement agencies should investigate specific issues and whether or not our antitrust laws need improvement to better promote competition in the digital markets,” said Rep. Doug Collins (R-GA), the top Republican on the House Judiciary Committee.

The committee is asking for communications to and from top executives at each company — including Mark Zuckerberg, Sheryl Sandberg, Larry Page, Sundar Pichai, Jeff Bezos, Tim Cook and others. Lawmakers want to see emails, texts, and encrypted messages, on a range of topics.

They ask each company to detail the marketshare of their platforms, products and services along with their top competitors and customers. The committee also asks for documents pertaining to antitrust issues, past litigation and investigations.

In a letter to Facebook, the committee asks for documents pertaining to the acquisitions of Instagram, WhatsApp and Onavo. Lawmakers also want to know about the decision to integrate Instagram, Facebook Messenger and WhatsApp.

In the letter to Alphabet CEO Larry Page, the lawmakers demand information concerning the acquisitions of YouTube, DoubleClick, Android and others. Lawmakers also ask Alphabet CEO Larry Page several questions about Google’s advertising practices and search results.

Lawmakers are looking for more information about a slew of Amazon acquisitions — including Audible, Whole Foods and Zappos. They also are probing the company’s pricing, advertising policies and search rankings for products sold on the site.

According to the letter sent to CEO Tim Cook, the committee appears most interested in Apple’s app store.

So far, the committee has held two public hearings as part of the investigation. Representatives from all four companies testified in July.

“I appreciate the willingness of certain tech companies to come before our committee and answer questions. However, we still need more information about their business practices at this fact-finding stage of this investigation,” said Rep. Jim Sensenbrenner (R-WI).

But after the July hearing, Cicilline slammed Google, Facebook and Amazon for their “evasive” answers. In an interview earlier this year, Cicilline told Yahoo Finance he would likely question the companies’ CEOs as part of the investigation.

The document request marks an escalation of the committee’s investigation, as the tech companies face mounting pressure from other antitrust enforcers. The FTC, DOJ and state attorneys general are all looking the companies’ practices.

On Monday, the attorneys general of 48 states, the District of Columbia and Puerto Rico announced an antirust probe into Google. Last week, another group of state attorneys general announced it was investigating Facebook.

House Judiciary’s antitrust subcommittee was scheduled to hold its third hearing this week, but postponed it to an unannounced date.

Amazon, Facebook, Google and Apple did not immediately respond to request for comment.

The committee wants answers from the tech giants by Oct. 14.

Jessica Smith is a reporter for Yahoo Finance based in Washington, D.C. Follow her on Twitter at @JessicaASmith8.

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