Supreme Court petition could reshape antitrust rules for online property platforms

CoStar Group asked the U.S. Supreme Court on December 10 to take up a dispute with Commercial Real Estate Exchange Inc. that challenges how antitrust law treats refusals to deal in the digital era. The petition seeks review of a 9th U.S. Circuit Court of Appeals decision that reinstated CREXi's claims that CoStar unlawfully restrained competition by locking brokers into its platforms and denying rivals access to key web tools.

CREXi alleges that CoStar used its market position to withhold technological access that rivals need to compete effectively, a claim the 9th Circuit found sufficiently plausible to revive. CoStar argues the appeals court created a new rule that could force companies to share proprietary software even when contracts are expressly non exclusive, and that such a rule would choke investment in product development and innovation.

The filing frames a narrow legal question with broad economic consequences. At issue is whether a firm can be compelled to deal with a competitor when its commercial agreements are non exclusive and when the firm has independently chosen not to provide access to certain services. The company asks the high court to clarify the scope of the refusal to deal doctrine and whether the line drawn by the 9th Circuit departs from Supreme Court precedents on compelled access.

The stakes extend beyond the two companies. Commercial real estate listings and brokerage tools are increasingly digital, and access to platforms, application programming interfaces and data feeds can determine which firms gain traction. If the Supreme Court adopts CoStar's view, dominant platform owners would face a narrower antitrust exposure when they withhold access to proprietary tools. That outcome could protect returns on software investment and preserve strong incentives for firms to develop and monetize specialized technology.

If the court sides with CREXi and sustains a broader compelled access rule, technology incumbents could face new obligations to share core functions with rivals. That result could lower entry barriers for challengers and promote competition in the short term, but it could also reduce the expected payoff from investing in costly, differentiated features. Policymakers and investors will weigh those trade offs as the case advances.

Antitrust scholars and industry participants will also watch how the court balances concerns about market power and foreclosure against the potential chilling effect on innovation. The case arrives as regulators and courts worldwide are wrestling with competition policy for online platforms, from search and social media to e commerce and financial infrastructure.

The Supreme Court takes only a fraction of the petitions it receives, and it will first decide whether the case raises sufficiently important legal questions to warrant review. If it accepts the petition, the resulting decision could produce a definitive rule on compelled access that shapes litigation strategy, regulatory priorities and investment choices across digital markets for years to come.

Reporting by Mike Scarcella; Dec. 10, 2025.