The escalating legal battle between two of the largest commercial real estate data firms, CoStar and Xceligent, has reached two of the world's largest brokerage firms.

CBRE and Newmark Knight Frank were both served subpoenas related to the lawsuits, The Real Deal first reported.

The subpoenas, filed Wednesday in the U.S. District Court for the Western District of Missouri, were requested by Xceligent. They order CBRE and NKF to produce any contracts, agreements or communications they had with CoStar or LoopNet, its public listing platform, that took place between Aug. 29, 2007, and the present.

In response, CoStar criticized the subpoena as unnecessary to the case.

“CoStar’s lawsuit against Xceligent has nothing to do with our customers," the company said in a statement provided to Bisnow. "The suit is about Xceligent’s industrial-scale theft of CoStar’s content. Regrettably, Xceligent is dragging our customers into the fray by forcing them to produce records from their files, while simultaneously suggesting that they do not know or maintain their own listing information, which is simply untrue.”

Xceligent defended the subpoenas as a routine evidence gathering method.

“This is an ordinary part of the litigation process," a company spokesperson said in a statement to Bisnow. "Xceligent’s goal is to gather all of the information necessary to protect the industry’s right to share data.”

CBRE and NKF declined to comment.

The legal battle kicked off in December when CoStar sued Xceligent, alleging widespread theft of its proprietary content. After seven months of silence, Xceligent responded in June with a countersuit that alleged CoStar engaged in years of anticompetitive behavior and violated federal antitrust laws.

The subpoenas are requesting information that could help support its antitrust claims, including whether CoStar threatened to raise its fees or terminate contracts with its clients if they worked with competitors. Xceligent is also targeting data CBRE and NKF provided to CoStar, including whether CoStar applied its watermark to photos the brokerages provided.

CoStar has pledged to spend up to $20M on the lawsuit this year, and Xceligent said its investors are willing to spend as much as it takes to win the case.

Last week, CoStar moved to dismiss the June antitrust suit, and said it was a "smokescreen to distract from Xceligent's own wrongdoing." After the motion, Xceligent said it stands by its claims and plans to see the case through.