The sweeping federal antitrust case against Google has given rise to a significant fight over data held by Microsoft, and the company is now facing a subpoena for millions of documents that could shed light on its attempts to compete with Google’s search engine. Having initially cooperated with prosecutors in building an antitrust case against Google, Microsoft could be obligated to produce millions more documents at the request of Google’s defense team.

At a status hearing on Friday morning, Judge Amit Mehta heard arguments from both Google and Microsoft on the issue, but ultimately found more information was required before the court could give guidance as to how much internal data Microsoft would be required to produce.

“These are hard issues for any judge to resolve in a way that’s objective and meaningful,” Mehta told attorneys, “and that’s particularly so given that, with respect to the additional custodians, I don’t have any sense of the volume that would produce … or what that volume would mean for the timing of production.”

Filed in October 2020, the Department of Justice’s antitrust case against Google focuses on anti-competitive behavior in search and search advertising, alleging among other claims that the company’s exclusivity agreements on Android and iOS shut out competing search engines. Separate antitrust cases against Google have also been filed focusing on the company’s browser privacy settings and alleged manipulation of search results.

In advance of the Department of Justice filing charges, Microsoft provided more than 400,000 documents to civil investigative demands from prosecutors. In a filing before today’s hearing, Google argued that participation entitles the company to a similar range of documents that might be helpful to its defense.

“No third party is more central to this litigation than Microsoft. The DOJ and Colorado Complaints refer to it or its products dozens of times,” Google’s filing reads. “Having so obviously pressed for and cooperated in the preparation of the present Complaints to be filed against Google, Microsoft cannot credibly avoid significant discovery in these cases.”

Google first issued a subpoena to Microsoft in April, seeking “older documents that will shed light on whether Microsoft was actually restrained from competing with Google, or whether it simply failed to compete successfully on the merits.” But Microsoft agreed to only eight of the 27 executives to be searched, and drastically limited the search strings to which they would be subject. Google is now asking for a more powerful court order to compel the production of documents from Microsoft.

In an appendix to its filing, Google listed 19 current and former Microsoft executives who may hold communications relevant to the case, including former Windows Phone chief Andrew Lees and former Windows head Terry Myerson.

“These executives cover issues at the core of the case: the development and distribution of Microsoft’s various search engines, Microsoft’s search advertising business, and Microsoft’s effort to market devices that would give it yet more search access points beyond the ever-present Windows desktop,” the filing reads. “Google simply seeks discovery commensurate with Plaintiffs’ allegations, which reach back two decades.”

In its own filing, Microsoft pushed back against this logic, arguing Google is filing unnecessarily broad requests in an effort to additionally delay the case. “In the past nine days, in fact, Google has proposed seventeen additional custodians,” Microsoft’s filing claims, “including nine on July 19, five on July 26, and three today, July 27. Google has not explained why it believes searching these additional twenty-eight custodians … is necessary.”

Weighing the two arguments, the court seemed to slightly favor Google’s side of the case, but ultimately asked for more data on the burden required to produce the documents. “The description of the people [Google has] identified as additional custodians certainly struck me as not reaching,” Judge Mehta said, “and I haven’t heard Microsoft say today that there’s minimal chance that they’re likely to have records at all that are responsive and relevant.”

However, the court ultimately found there was insufficient information about the burden posed by production, and the dispute is likely to continue at least until August 20th, the deadline set for further filings on the subject.

“The best I can do for you today is to give you a deadline by which to get back to me with concrete information,” Judge Mehta told the parties.

The finding is one more turn in what is likely to be a long and contentious discovery period for the antitrust case. Microsoft says it believes the first phase of its own document production will last until at least October of this year. Trial proceedings for US v. Google are scheduled to begin on September 12th, 2023.