Crexi's antitrust claims against CoStar can officially move forward in the lower court.

The U.S. Supreme Court has declined to review a petition by CoStar challenging a ruling by the appeals court that reopened claims that CoStar is a monopoly.

Last June, the U.S. Court of Appeals for the 9th Circuit found that commercial real estate marketplace operator Crexi "plausibly" argued that data platform CoStar's practices violate the Sherman Antitrust Act. The decision overruled a district court’s dismissal of the case and ordered it to reconsider Crexi's argument.

CoStar filed a petition in December asking the Supreme Court to review the appeals court decision.

The competitors have been at each other in court since 2020, when CoStar sued Crexi for copyright infringement. It alleged that Crexi stole CoStar’s intellectual property, including thousands of photos, to operate its business.

Crexi filed a countersuit that year, alleging that CoStar’s methods of not allowing competitors to access its platforms and blocking brokers from uploading listings on a competing platform hurt competitors and raised operation costs.

CoStar argued that it doesn’t have to let competitors use its platform and that letting Crexi's case move forward disincentivizes investment into data businesses.

"CREXi's antitrust counterclaims are a sideshow to CoStar Group's underlying mass copyright infringement claims against CREXi," CoStar General Counsel Gene Boxer said in a statement Monday in response to the Supreme Court's decision.

Boxer said Crexi's antitrust claims won't delay CoStar's intentions to move forward with a copyright infringement trial.

"CoStar has run out of delay tactics now that the Supreme Court rejected its failed appeal," a representative for Crexi said in a statement Tuesday. "CoStar’s antitrust violations — well known to the CRE industry for years — will finally be scrutinized in court. Crexi looks forward to aggressively pursuing our antitrust claims."

If the Supreme Court had agreed to hear the case, it could have set a precedent for antitrust laws in the digital marketplace. The court's decision to kick it back to the lower court could leave the door open for similar cases down the line.

CoStar also faced a monopoly case from competitor Xceligent in 2017, though that died when Xceligent went bankrupt that year. The Federal Trade Commission blocked CoStar from acquiring RentPath in 2020 over antitrust concerns and forced CoStar to spin off a subsidiary — Xceligent — before it could acquire LoopNet in 2012.