On Monday, U.S. attorneys argued that Google had established a monopoly over online ad placement services, concluding an antitrust trial that could intensify the company’s legal challenges amid its dominance in advertising technology.

The case centers on the software system used by advertisers to place ads across websites. Aaron Teitelbaum, representing the Justice Department, argued before Judge Leonie M. Brinkema of the U.S. District Court for the Eastern District of Virginia that Google had interconnected its products in such a way that it made it nearly impossible for publishers and advertisers to use alternatives.

“Google is a monopolist—time and again,” Teitelbaum said. “These are the markets that ensure a free and open internet.”

In response, Google’s lead attorney, Karen Dunn, contended that the government had failed to present adequate evidence and was on unstable legal grounds. “Google’s actions reflect innovation in response to competition,” she stated.

The case marks the conclusion of the U.S. government’s antitrust lawsuit, filed against Google by the Justice Department and eight states last year. (Additional states have since joined the suit.) The government accuses Google of misusing its control over ad technology, partly through its 2008 acquisition of the ad-tech company DoubleClick. Judge Brinkema is now set to rule on the merits of the case in the coming months.

Google has faced increasing scrutiny over its vast influence in technology markets, with multiple antitrust cases filed against it in recent years. In August, a landmark ruling found that Google had violated antitrust laws to preserve its dominance in online search. The Justice Department has even requested that Google be split up, including a proposal to force it to divest Chrome, the world’s leading web browser, with a deadline of December 20 for Google to propose alternatives.

The ad-tech case, if successful, could deliver another significant blow to Google. The government has already called for a breakup of the company’s ad-tech division, which generated $31 billion in revenue last year—about 10% of Google’s total income. If Judge Brinkema finds that Google has unlawfully stifled competition, she could order the company to spin off its ad-tech operations and impose further restrictions. However, this division is only part of Google’s advertising business, which also includes search ads, YouTube video ads, and paid promotions on Google Maps.

A ruling against Google could set a precedent for other high-profile antitrust cases against major tech companies. The Justice Department is also pursuing legal action against Apple, while the Federal Trade Commission has sued Amazon and Meta for anticompetitive practices.

During a three-week trial in September, the government argued that Google holds an 87% market share in ad-tech, enabling it to capture a larger portion of each sale and disadvantage publishers and website owners. Testimonies included those from Google executives, such as YouTube’s Neal Mohan, and from industry veterans like News Corp’s representatives.

Teitelbaum, representing the Justice Department, accused Google of using its market power to link its technologies, enriching itself at the cost of other businesses. Judge Brinkema asked several probing questions during the closing arguments, particularly regarding Google’s internal communication policies. However, she did not indicate a clear direction for her final ruling.

In one hypothetical scenario, Judge Brinkema asked what would happen if a company produced the best product and customers flocked to it instead of its competitors, potentially creating an anticompetitive situation. Teitelbaum argued that this scenario described healthy competition. He added that products which might have challenged Google’s dominance had often failed due to the company’s monopolistic tactics.

Google maintains that it faces significant competition in the ad-tech space, including from newer players such as social media platforms. Dunn, defending Google, argued that the evidence did not support the government’s claims and that the company had introduced innovative products. Over the period in question, she noted, ad prices had decreased, spending had increased, and the quality of ads had improved—an outcome she argued was the opposite of what one would expect from monopolistic behavior.

In the government’s rebuttal, lead attorney Julia Tarver Wood countered Google’s claim, pointing out that while some witnesses suggested publishers could create their own alternatives to Google’s services, such efforts would be prohibitively costly. Bill Kovacic, a former FTC chair, emphasized that the Justice Department’s success in challenging Google, particularly in both search and ad-tech cases, would solidify its credibility and set a significant precedent for future antitrust cases.