U.S. enforcers notched a historic antitrust victory against tech giant Google on Monday, when a federal judge found the company illegally maintained a monopoly over internet search. It marked the most significant such defeat for a Silicon Valley behemoth in decades.

In his highly anticipated ruling, Judge Amit P. Mehta called Google a “monopolist” that squelched competition and raised advertising prices by leaning on “exclusive distribution agreements” that made its search engine the default option on phones and browsers. (Google said it planned to appeal. )

But government officials already face their next major test: getting the judge to sign off on competition-promoting changes to Google’s business practices.

Mehta is about to decide what a remedy for Google’s unlawful conduct should look like. That sets up another clash that could have massive implications for not only the company but consumers and competitors alike.

The Justice Department and a coalition of states have not outlined which remedies they may seek, but the topic was a matter of intense speculation even before the case went to trial last fall.

One of the most forceful actions the judge could take is to require Google to split off its search engine from other parts of its business, like its Chrome browser or Android operating system, antitrust lawyers said.

“Breaking them up may be the first choice if it’s possible, but courts are very reluctant to even consider such an extreme remedy unless there’s no other options on the table,” said Tara Pincock, policy counsel at the anti-monopoly group Open Markets Institute.

Pincock, who worked on the Google case as an assistant attorney general for Utah, said Mehta might instead consider “conduct remedies” that alter the company’s practices without forcing a breakup, such as requiring that the company terminate its distribution deals with companies like Apple.

“The most obvious remedy is an end to Google’s exclusive defaults with various browsers and device manufacturers, but that alone won’t cure the market of Google’s scale benefits,” said Lee Hepner, senior legal counsel for the advocacy group American Economic Liberties Project.

Adam Kovacevich, a former Google executive and founder of the left-leaning tech trade group Chamber of Progress, argued that such a change wouldn’t have the practical effect enforcers are seeking. And the biggest winner from it, he said, would likely be rival tech giant Microsoft, which could make gains in the market if Google is barred from bidding to be the default search engine on other digital products.

Should that remedy be imposed, Kovacevich said, Google “is probably going to be fine because it’ll probably be chosen by a lot of people still, even if it’s not the default.” His group counts Google, Meta and Amazon as members. (Amazon founder Jeff Bezos owns The Washington Post.)

Antitrust lawyers said the judge may also weigh more modest options, such as forcing Google to license parts of its search business, or present users with a so-called “choice screen” that offers alternative defaults for their browsers.

The company has rolled out similar screens in response to regulatory pressure in Europe, but there are lingering questions about how effective they have been in opening up competition.

“We just need to focus on the fact that we have to restore competition to this market, and whatever remedies that are on the table, that should be what’s front of the mind,” Pincock said.

Cristiano Lima-Strong is a tech policy reporter and co-author of The Washington Post’s Tech Brief newsletter, focusing on the intersection of tech, politics and policy. His coverage focuses on privacy and children’s online safety. He previously served as a senior web producer, breaking news reporter and tech policy reporter for Politico.