There's a $30 billion reason the Google antitrust ruling will have the search giant very worried right now

• Google projected it could lose $30 billion if it lost its default spot on Apple devices.
• A federal judge ruled that Google's agreements with Apple and others "have anticompetitive effects."
• A breakup with Apple is just one potential remedy. Google said it plans to appeal.

Google's agreements with Apple and other companies to be their default search engine have violated antitrust law, a federal judge ruled on Monday .

"Google is a monopolist," wrote US District Judge Amit P. Mehta in the ruling , "and it has acted as one to maintain its monopoly."

The Department of Justice's case centered on Google's payments to other companies, like Apple and Samsung, to give its search engine prominence on their devices.

For Google, there's apparently a very good reason to keep these payments coming, as the search revenue generated is worth billions.

According to Monday's filing, the company estimated in 2017 that its default placements across Safari, Firefox, and other browsers drove 54% of its search revenue. That number has only increased.

In particular, Google has a major deal with Apple to keep Google the default search engine on Safari, which runs on iPhones, iPads, and Mac computers worldwide.

In 2020, Google projected that it would lose between 60% and 80% of its search volume on Apple devices if it were replaced as the default general search engine, the filing said. That accounts for between $28.2 billion and $32.7 billion in net revenue losses, it added.

"Google's distribution agreements are exclusive and have anticompetitive effects," Mehta wrote.

Eddy Cue, senior vice president of services at Apple, revealed in court documents earlier this year that Google paid $20 billion in 2022 to secure this spot, which amounted to 17.5% of Apple's operating income. So, any remedy that stops or reduces Google's search payments would be bad news for Apple, too .

The landmark decision on Monday marked the near-conclusion of the DOJ's lawsuit against the search company, which was filed in 2020.

What happens next is still unknown, as the ruling did not include remedies.

Google's president of global affairs, Kent Walker, told Business Insider in a statement that the company plans to appeal; this could be drawn out for a while longer.

The ruling will undoubtedly have Google leaders concerned, particularly if remedies include forcing it to break up with Apple.

Some experts previously floated a worst-case scenario for Google where it's barred from bidding for the default position on devices while competitors still can, although this may be an extreme scenario.

Even so, anything that pushes Google out of that default spot on Apple's devices could be very bad news for the search giant — and it knows it.

Are you a Google employee? Got a tip? You can contact this reporter securely on Signal at hughlangley.01 or email at hlangley@businessinsider.com .