After beating back a United States Justice Department challenge to its search monopoly, Google is now confronting a new legal test targeting its grip on digital advertising.

The case, opening Monday in federal court in Alexandria, Virginia, centers on allegations that Google’s ad technology amounts to an illegal monopoly. U.S. District Judge Leonie Brinkema has already found parts of the system unlawful, ruling that Google’s practices stifle competition and disadvantage online publishers that depend on ad revenue.

Google and the U.S. Justice Department will spend the next two weeks in a “remedy” trial aimed at determining how to restore competition in the digital ad market, with U.S. District Judge Leonie Brinkema expected to issue a ruling after further filings and arguments extend into November.

A decision is unlikely before year-end.

Google has already vowed to appeal Brinkema’s earlier finding that its ad network is an illegal monopoly, though an appeal cannot be filed until the remedy is finalized.

The case, brought in 2023 under President Joe Biden’s administration, poses a direct challenge to the ad tech system Google has built over 17 years.

Digital advertising, which fuels most of the $305 billion in revenue from Google’s services arm, not only underpins Alphabet Inc.’s business but also sustains thousands of websites reliant on ad sales.