Alphabet's Google illegally dominated two markets for online advertising technology, a federal judge said on Thursday, dealing another blow to the tech titan in an antitrust case brought by the U.S.

Shares of Alphabet fell 3% on the news.

The ruling by U.S. District Judge Leonie Brinkema in Alexandria, Virginia, could allow prosecutors to argue for a breakup of Google's advertising products. The U.S. Department of Justice has said that Google should have to sell off at least its Google Ad Manager, which includes the company's publisher ad server and its ad exchange.

Google will now head in to 2025 facing the possibility of two different U.S. courts ordering it to sell assets or change its business practices, as a judge in Washington will hold a trial in April on the DOJ's request to make Google sell its Chrome browser and take other measures to end its dominance in online search.

Google has previously explored selling off its ad exchange to appease European antitrust regulators, Reuters reported in September.

Brinkema oversaw a three-week trial where the DOJ and a coalition of states sought to show Google monopolized markets for publisher ad servers and advertiser ad networks, and tried to dominate the market for ad exchanges which sit between buyers and sellers.

Google used classic monopoly-building tactics of eliminating competitors through acquisitions, locking customers in to using its products, and controlling how transactions occurred in the online ad market, prosecutors said at trial.

Google argued the case focused on the past, when the company was still working on making its tools able to connect to competitors' products. Prosecutors also ignored competition from technology companies including Amazon.com and Comcast as digital ad spending shifted to apps and streaming video, Google's lawyer said.