WASHINGTON (Reuters) - A much-anticipated deep dive into antitrust allegations against four of America’s largest tech companies and recommendations on how to tame their market power could be released by late summer or early fall from the House of Representatives Judiciary Committee’s antitrust panel, senior committee aides said.

The committee has received 1.3 million documents from the companies so far, they said in a call with reporters on Thursday.

The panel will question the CEOs of Facebook Inc (FB.O), Amazon.com Inc (AMZN.O), Google parent Alphabet Inc (GOOGL.O) and Apple Inc (AAPL.O) as part of its investigation into whether the companies’ business practices hurt smaller rivals. The hearing was supposed to be held on July 27 but has been delayed.

On Thursday, Reuters reported that the chief executives will defend themselves by saying their companies face intense competition and by pushing back against claims they are dominant.

All four companies will testify voluntarily and no subpoenas have been issued, the committee aides said.

In May, Representative David Cicilline, chair of the Judiciary Committee’s antitrust panel, had demanded Jeff Bezos testify and threatened Amazon with a subpoena, after reports surfaced Amazon employees tapped data from small sellers in the company’s marketplace to make decisions about the online retailer launching its own competing products, despite telling lawmakers it did not engage in such practices.

Addressing questions about the format of the high-profile hearing, the aides said, there will be a single panel with all four CEOs attending virtually. Members of the subcommittee led by Cicilline, however, will attend either in person or online.

“The number of rounds of questioning is up to the discretion of the chair,” said one committee aide.

Asked if the hearing would uncover new information, a senior aide said that despite the risk of companies not always answering questions fully it was important to hear from decision makers.

“This is not like a normal oversight hearing, where we hear from the CEO’s and move on.”