Wednesday should be a historic day. Mark Zuckerberg, Jeff Bezos, Tim Cook and Sundar Pichai — the CEOs of Facebook, Amazon, Apple and Google-owned Alphabet — are scheduled to sit before the House Judiciary Subcommittee on Antitrust. The hearing, which was initially scheduled for Monday, has been rescheduled for noon Eastern, as Axios first reported on Saturday morning.

A scheduling conflict was to blame for the delay. The late John Lewis, a Democratic representative and civil rights leader who died last week of pancreatic cancer, will lie in state in the Capitol Rotunda on Monday, it was announced on Thursday.

Months in the making, the antitrust hearing aims to have four of the most powerful CEOs in tech defend accusations of monopolistic behaviors. All four tech giants have faced scrutiny over the past year from lawmakers and regulators, who not too long ago looked at Silicon Valley in a far more positive light. Now officials are raising concerns about these companies’ growing dominance in the market, which could be squashing competition.

“Since last June, the subcommittee has been investigating the dominance of a small number of digital platforms and the adequacy of existing antitrust laws and enforcement,” House Judiciary Committee Chairman Jerrold Nadler and Antitrust Subcommittee Chairman David Cicilline said in a joint statement Saturday. “Given the central role these corporations play in the lives of the American people, it is critical that their CEOs are forthcoming. As we have said from the start, their testimony is essential for us to complete this investigation.”

During a committee hearing in January, smaller tech firms complained about unfair business practices from the tech giants. Sonos CEO Patrick Spence told lawmakers that Google tried to restrict his company’s innovations and wanted insights into Sonos’ future product plans. Sonos sued Google, claiming the company stole its wireless speaker technology. David Barnett, CEO of PopSockets, blasted Amazon for ignoring issues about counterfeit that he’d raised for months, bullying him to lower his prices.

“There’s such a dominant power that exists with these companies that really even as a company of our size you feel like you have no choice,” Spence said.

The process of getting all four CEOs in front of the committee was not without drama. Cicilline in May threatened to subpoena Bezos to appear at the antitrust hearing after sending an open letter to Bezos calling for his testimony. Bezos agreed to appear in June.

The hearing will stream live here.

CNET’s Richard Nieva and Michelle Meyers contributed to this report.