Alphabet's Google faces trial in a second antitrust case next week where the U.S. Department of Justice will challenge how the search giant monetises advertising through a system that prosecutors say harms news publishers. The case is part of the Biden administration's effort to rein in Big Tech through antitrust law, and follows a major win for the Justice Department in a separate lawsuit on Aug. 5 when a judge found that Google illegally monopolized online search.

While that case focused on Google's ubiquitous search engine, the trial beginning in Alexandria, Virginia, on Monday will home in on less conspicuous Google technology that connects website publishers and advertisers.

Those advertising tools contributed to the more than 75% of Google's $307.4 billion in revenue last year that came from advertising.

"Google is far and away the largest seller of advertising on earth. They touch every part of the industry, if not directly, then indirectly. Everyone has an interest in Google one way or another," said Brian Wieser, an advertising consultant and financial analyst. The Justice Department and a coalition of states will seek to show Google broke U.S. antitrust law in its digital advertising businesses. A victory for the states and Justice Department would set the stage for them to ask U.S. District Judge Leonie Brinkema to order a breakup of the company.

The antitrust regulators accuse Google of dominating the markets for the technology behind website ads by tying its tools for publishers and advertisers together, staking out a "privileged position as the middleman."

Google has denied the claims, saying it is not required to share technological advantages with rivals and that its products are interoperable with those offered by competitors.

The Justice Department alleges that Google controls 91% of the market for ad servers, where publishers offer ad space, more than 85% of the market for ad networks, which advertisers use to place ads, and over half of the market for ad exchanges.

Google says its share of those markets is 30% or less when including advertising on social media, streaming TV and apps, and says the Justice Department's narrow focus on website ads obscures the fierce competition it faces as those categories grow.

Google competitors on the advertiser side, such as Trade Desk and Comcast, and publisher side, such as PubMatic, are on the list of potential witnesses.

The case will also highlight how advertising technology has affected news organizations. One-third of newspapers in the U.S. have been closed or sold since 2005, according to a Northwestern University study published last November.

"Journalism is under threat in large part due to consolidation in the advertising market," Justice Department antitrust chief Jonathan Kanter said at an event held in June by the Open Markets Institute, an anti-monopoly advocacy group.

Current or former executives from News Corp, the Daily Mail and Gannett, which has also sued Google, may testify at trial.

Google has focused on small businesses and publishers, some of whom it plans to call as witnesses at trial. A breakup would "slow innovation, raise advertising fees, and make it harder" for small companies to grow, Google has said.

The way Google viewed its ad tech will be a key focus at trial, with potential testimony from more than two dozen current or former employees and executives, including YouTube Chief Executive Neal Mohan, a former Google advertising executive.