WASHINGTON — Attorneys from Dallas-based AT&T and the Justice Department volleyed back and forth Monday, arguing whether the government should be permitted to use boxes of AT&T internal emails and documents about other major mergers to build its case.

The debate over the potential court exhibits kicked off a pivotal week for AT&T, which is seeking to buy Time Warner Inc. and become a media and entertainment powerhouse. The antitrust trial drew dozens of reporters, law students and antitrust attorneys who waited for hours to pack into rows of seats in a wood-paneled courtroom. Opening arguments will begin Wednesday. The trial is expected to last six to eight weeks.

The arguments on Monday indicate that the Justice Department's case will hinge, at least in part, on AT&T's own emails and that they may include some illuminating or explosive information. During the trial, regulators will argue that the AT&T-Time Warner merger, which is valued at nearly $109 billion including debt, would harm competition and raise prices for consumers.

U.S. District Judge Richard Leon will rule on whether the contentious exhibits — which include AT&T employees' emails and slideshow presentations, DirecTV statements about the NBCUniversal-Comcast Corp. merger and a Google presentation about the importance of Time Warner-owned programming to YouTube TV— will be admitted in the case.

Leon said he'd like to clear up which documents are relevant ahead of Wednesday's opening arguments. He said some emails should be admitted as business records. Others, he said, resemble chatter that "used to happen at the water cooler." He said he's more inclined to include emails or slides if a witness can provide context, such as explaining who authored the slideshow and whether it was a first draft or a major presentation.

In his argument before Leon, Justice Department attorney Eric Welsh said the emails and slides help explain AT&T's business strategy and why it sought to acquire Time Warner.

Another point of contention is the possible inclusion of documents and statements about prior mergers, such as the NBCUniversal-Comcast merger. The merger has been frequently compared to the AT&T-Time Warner merger because it married a cable company and a large provider of TV programming and movies. It was also a vertical merger, a deal that combines two companies that are not direct competitors.

One of the documents is a statement by DirecTV, which has since been acquired by AT&T, about the harms of the vertical merger of NBCUniversal and Comcast.

AT&T attorney Daniel Petrocelli said the DirecTV statement is irrelevant because it was made by the company years before it was bought by AT&T. And, he said, the comment is outdated in a media and entertainment landscape that changes at "warp speed."

Petrocelli challenged the use of some internal AT&T emails, too. In one case, he said, the government wants to use emails sent by a low-level employee whose ideas were later rejected by AT&T's top executives.

But Welsh said the emails and slideshows reveal the inner workings of AT&T and its business strategy. He said the majority of them were sent by or created by "folks who have been in the organization for years." He compared some of the emails and email chains to conference room discussions in the digital age.

Lawyers from the Justice Department and AT&T asked Leon what information could be kept confidential during the trial. Welsh asked if the Justice Department could question some AT&T and third-party witnesses in closed session. He said the third-party witnesses will testify about their fears of higher prices if the AT&T-Time Warner merger is approved but said they want sensitive business information to remain private.

Welsh said AT&T has labeled many paragraphs, pages and even whole documents confidential, which would keep the Justice Department from asking important questions in open court.

Petrocelli rejected that description, saying many times the confidential information is "just a fact or figure." He said AT&T and third-party witnesses, most of who are testifying views that benefit the government, should be held to the same standards with confidentiality.

Leon pushed both attorneys to pare down the documents and figures they consider confidential before court resumed Tuesday. He said he's not in "the secret forum business," and a trial of such magnitude should play out in public.