The lawsuit is Google's second such test this year after the California-based tech juggernaut saw a similar government demand to split up its empire shot down by a judge earlier this month.

Monday's case focuses specifically on Google's ad tech "stack" -- the tools that website publishers use to sell ads and that advertisers use to buy them.

In a landmark decision earlier this year, Federal Judge Leonie Brinkema agreed with the US Department of Justice (DOJ) that Google maintained an illegal grip on this market.

Monday's trial is set to determine what penalties and changes Google must implement to undo its monopoly.

According to filings, the US government will argue that Google should spin off its ad publisher and exchange operations. The DOJ will also ask that after the divestitures are complete, Google be banned from operating an ad exchange for 10 years.

Google will argue that the divestiture demands go far beyond the court's findings, are technically unfeasible, and would be harmful to the market and smaller businesses.

"We've said from the start that DOJ's case misunderstands how digital advertising works and ignores how the landscape has dramatically evolved, with increasing competition and new entrants," said Lee-Anne Mulholland, Google's Vice President of Regulatory Affairs.

In a similar case in Europe, the European Commission, the EU's antitrust enforcer, earlier this month fined Google 2.95 billion euros ($3.47 billion) over its control of the ad tech market.

Brussels ordered behavioral changes, drawing criticism that it was going easy on Google as it had previously indicated that a divestiture may be necessary.

This remedy phase of the US trial follows a first trial that found Google operated an illegal monopoly. It is expected to last about a week, with the court set to meet again for closing arguments a few weeks later.

The trial begins in the same month that a separate judge rejected a government demand that Google divest its Chrome browser, in an opinion that was largely seen as a victory for the tech giant.

That was part of a different case, also brought by the US Department of Justice, in which the tech giant was found responsible for operating an illegal monopoly, this time in the online search space.

Instead of a major breakup of its business, Google was required to share data with rivals as part of its remedies.

The US government had pushed for Chrome's divestment, arguing the browser serves as a crucial gateway to the internet that brings in a third of all Google web searches.

Shares in Google-parent Alphabet have skyrocketed by more than 20 percent since that decision.

Judge Brinkema has said in pre-trial hearings that she will closely examine the outcome of the search trial when assessing her path forward in her own case.

These cases are part of a broader bipartisan government campaign against the world's largest technology companies. The US currently has five pending antitrust cases against such companies.

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