Judge Blocks CoStar From Weighing In on the Zillow–MRED–Compass Fight

On June 16, Illinois federal judge John Tharp denied CoStar's motion to file an amicus curiae brief in the antitrust lawsuit Zillow brought against Midwest Real Estate Data (MRED) and Compass. The one-sentence ruling came without explanation. A hearing on Zillow's underlying motion for a preliminary injunction is scheduled for early July.

The denial keeps the courtroom fight squarely between its three original combatants — and does nothing to slow a dispute that has real consequences for anyone planning to list a home this year.

How This Fight Started and Where It Stands Now

Zillow filed suit in mid-May, accusing MRED — the MLS serving the Chicago region — and Compass of conspiring to pressure Zillow into displaying listings that allegedly violate its own policies. Zillow's rules have targeted what it calls private or "hidden" listings: properties marketed within a brokerage's internal network before appearing publicly.

MRED followed through on a threat to cut Zillow's direct listing feed, arguing Zillow was selectively censoring submissions from Compass brokers. A temporary restraining order is currently in place requiring MRED to keep supplying Zillow with listing data, while Zillow is barred from blocking any MRED listings on its platform. That standoff is what the July hearing will address.

Meanwhile, Realtracs, the dominant MLS in Nashville, has signaled it may follow MRED's lead. As of June 16, the two parties were still negotiating, and Zillow's full Nashville feed remained live.

What CoStar Wanted the Court to Hear — and Why the Judge Said No

CoStar, the parent company of Homes.com, argued it had a direct stake in the outcome. In its proposed brief, the company contended that Zillow was being inconsistent: suing to guarantee its own access to MLS data while simultaneously running Zillow Preview, a feature launched in mid-March that lets agents pre-market listings on Zillow's platform before those properties go to active status. CoStar argued that arrangement effectively walls off pre-market inventory from competing portals like Homes.com.

Gene Boxer, CoStar's general counsel, said in a statement that Zillow "cannot claim to be defending openness and transparency while building a system that advantages Zillow, withholds inventory from competing platforms and undermines the very principles it invokes in court." Zillow pushed back, with a spokesperson stating that Zillow Preview listings are visible to any shopper at no cost, and that CoStar and Compass were conflating pre-marketing with private marketing.

Judge Tharp sided with neither argument — at least not explicitly. He denied the motion without elaborating, leaving CoStar on the sidelines for the July hearing.

Why Sellers Should Watch the July Hearing Closely

This lawsuit is not a procedural sideshow. Its outcome will directly influence which platforms receive MLS listing feeds, how quickly your property gets in front of buyers, and whether pre-market strategies remain a viable option for sellers working with certain brokerages.

Here is what is at stake in concrete terms:

• Listing visibility: If courts or MLS boards restrict how portals receive data feeds, your home may not appear simultaneously on all major search platforms. Gaps in coverage translate to fewer buyer eyeballs during the critical first days on market.
• Pre-market options: The legality and enforceability of pre-marketing strategies — coming-soon periods, office exclusives, network-first launches — are at the center of this case. A ruling against Compass and MRED could narrow those options. A ruling in their favor could expand them.
• Portal competition: Zillow, Homes.com, and their rivals are fighting over where buyers search. More competition between portals generally benefits sellers by broadening distribution. A court decision that consolidates data access with one dominant player would move in the opposite direction.

For now, sellers in MRED's coverage area — the Chicago metro — are in the most direct line of fire. The temporary restraining order keeps Zillow's feed intact through the July hearing, so listings there are still reaching Zillow buyers. But that status is not permanent. If the court lifts the restraining order at the July hearing and allows MRED to cut the feed again, Chicago-area sellers working with agents who syndicate through MRED would need to confirm their listings are reaching Zillow through an alternative syndication path, or accept reduced portal coverage.

Sellers outside Chicago should not assume they are insulated. The Realtracs situation in Nashville is unresolved, and the broader question of whether MLSs can selectively cut portal feeds — and under what circumstances — will likely be answered by this case in a way that applies nationally.

If you are weighing a sale in the next few months, ask your agent directly: how does your listing get to each major portal, what happens if an MLS suspends a feed, and do you have backup syndication in place? Those are no longer hypothetical questions. If you want a baseline sense of your home's value that doesn't depend on any single portal's data, our instant-offer tool runs independently of the MLS feed disputes currently in play.