The length of the hearing may also be prolonged since the antitrust issues facing Apple, Facebook, Google and Amazon are complex and vastly different.
Amazon is accused of abusing its role as both a retailer and a platform hosting third-party sellers on its marketplace. Apple has been accused of unfairly using its clout over its App Store to block rivals and to force apps to pay high commissions. Rivals have said Facebook has a monopoly in social networking. Alphabet, the parent company of Google, is dealing with multiple antitrust allegations because of Google’s dominance in online advertising, search and smartphone software.
Democrats may also veer off the topic of antitrust and bring up concerns about misinformation on social media. Some Republicans are expected to sidetrack discussion with their concerns of liberal bias at the Silicon Valley companies and accusations that conservative voices are censored.
“There was an attitude these were great American companies that created jobs and that we should have a hands-off approach and let them flourish,” Mr. Cicilline said in an interview. “But there are a lot of serious issues we have uncovered over the course of the investigation that weren’t apparent when we first began investigating.”
Facebook, Amazon, Google and Apple declined to comment.
For the chief executives, the hearing will be a test of how they perform under fire. Mr. Bezos, 56, has not previously testified to Congress, while Mr. Cook, 59, and Mr. Pichai, 48, have both testified once before. Mr. Zuckerberg, 36, the youngest of the group, has the distinction of being the veteran: He has answered questions at three congressional hearings in the past two years as Facebook has dealt with issues such as election interference and privacy violations.
But none are taking any chances for the event to go awry. Mr. Zuckerberg, who had been at his 750-acre estate on the Hawaiian island of Kauai, has been preparing for his testimony with the law firm WilmerHale, according to people with knowledge of the matter. And a small team is working with Mr. Bezos for his testimony in Seattle, said people with knowledge of the matter.
For weeks, the tech giants have also waged a lobbying battle to soften any blows. All four chief executives planned to call lawmakers on the House subcommittee in the days before the hearing, said three people with knowledge of the preparations who were not authorized to speak publicly.