Brokers, landlords sue CoStar alleging rental data monopoly
On June 15, 2026, brokers and landlords filed a class action accusing CoStar of monopolizing lease data.
Why it matters: Legal counsel should watch this case closely—it challenges data access and competition practices in commercial real estate, impacting transaction strategy and compliance with antitrust laws.
- Class action filed June 15, 2026, by major brokers and landlords against CoStar Group Inc.
- Lawsuit alleges CoStar limits competition by controlling essential commercial lease data access.
- CoStar sued Zillow in July 2025 for copying nearly 47,000 images, claiming deliberate copyright infringement.
- CREXi opposed CoStar’s February 2026 Supreme Court petition, arguing CoStar restricts broker competition via contracts.
On June 15, 2026, key commercial real estate brokers and landlords filed a class action lawsuit against CoStar Group Inc.. The plaintiffs accuse CoStar of monopolizing critical commercial lease data by enforcing exclusive contracts that block competitors from accessing this information.
This data is vital for brokers and landlords to evaluate leases and compete fairly. The complaint details how CoStar’s control over lease information restricts rival companies’ abilities, potentially violating antitrust laws designed to preserve market competition.
CoStar commands a dominant position, reporting 141 million average monthly unique visitors in Q2 2025 across its real estate platforms. This scale reinforces the impact restricting data access can have on the broader market.
The company's legal battles include a July 2025 copyright suit against Zillow over the unauthorized use of about 47,000 CoStar-owned images. CoStar’s general counsel, Gene Boxer, described Zillow’s actions as "deliberate mass infringement," emphasizing efforts to enforce copyrights through litigation.
Another dispute involves CREXi, which CoStar sued over content use in 2020. In February 2026, CREXi challenged CoStar’s petition for the U.S. Supreme Court to review pending antitrust claims. CREXi argued that CoStar’s broker contracts contain terms that hinder brokers from working with competitors, thereby restricting market competition.
In antitrust terms, the case raises questions about "market power"—the ability to control market conditions or exclude rivals. For legal professionals, these claims underscore the importance of scrutinizing data licensing terms and exclusivity agreements in real estate technology deals.
By the numbers:
- June 15, 2026 — Date of class action filing against CoStar
- 141 million — CoStar’s average monthly unique visitors in Q2 2025
- 47,000 — Number of images at issue in CoStar’s 2025 copyright suit against Zillow
Yes, but: CoStar denies the monopoly claims and argues that its contracts protect intellectual property rights and promote innovation.
What's next: The Supreme Court may decide soon whether to review CoStar’s petition, which could clarify legal standards around data access and antitrust in real estate tech.