Lawmakers on Friday made a sweeping bipartisan request for a trove of documents from Amazon, Apple, Facebook, and Google, ramping up the pressure on Silicon Valley’s largest and most powerful firms as they face questions of whether they suppressed competition in the tech industry.

The demand from Republican and Democratic members of the House Judiciary Committee comes as part of the panel’s antitrust investigation into the four companies. The probe seeks to examine competition problems in digital markets, whether the tech industry’s largest and most powerful companies are engaging in anticompetitive behavior, and whether existing mechanisms, such as antitrust laws, are adequate to address this conduct.

The lawmakers asked the companies to turn over financial statements for their products and services, communications from top officials at each company, including their chief executives, related to a range of topics, and documents produced as part of “any prior investigation or litigation” involving a federal or foreign entity related to anticompetitive practices.

“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,” House Judiciary Committee Chairman Jerry Nadler said in a statement.

The records requested from the four platforms, the New York Democrat said, will “provide the committee with a better understanding of the degree to which these intermediaries enjoy market power, how they are using market power, whether they are using their market power in ways that have harmed consumers and competition, and how Congress should respond.”

Georgia Rep. Doug Collins, the top Republican on the Judiciary Committee, said the 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.”

The antitrust investigation from the House Judiciary Committee is one of several big tech companies are facing. Attorneys general from almost all 50 states last week announced a probe into monopolistic practices by Google, and nine state attorneys general opened an antitrust investigation into Facebook.