SAN FRANCISCO — House lawmakers have asked more than 80 companies for information about how their businesses may have been harmed by Amazon, Apple, Facebook and Google, according to four people familiar with the requests.

The House Judiciary Committee, which is investigating the influence of the tech giants, sent formal requests for information to the companies on Sept. 13.

They were asked about their own businesses and how the four tech companies may have engaged in anticompetitive behavior, according to the people who have seen the requests and spoke on the condition of anonymity because the lawmakers asked to keep the letters private.

The bipartisan requests from the committee indicated the increasing scope of the congressional investigation into Silicon Valley’s power and offered more insight to the pressure Big Tech faces in the coming months. Similar inquiries are underway at the Justice Department, at the Federal Trade Commission and a bipartisan collection of attorneys general from dozens of states.