Zillow rival asks judge to deny injunction in MRED listings battle 

CoStar Group has decided to wade into the court battle between Zillow and a Chicagoland multiple listing service, saying that a decision in favor of Zillow would "reward" the search portal's "own anticompetitive conduct."

On June 10, CoStar filed an amicus curiae brief in the U.S. District Court for the Northern District of Illinois opposing Zillow's motion for a preliminary injunction in its lawsuit against Midwest Real Estate Data (MRED) and Compass. Zillow had asked the court to allow the portal to continue enforcing its listing access standards without retaliation, and to prevent MRED from cutting its listing feeds. 

The original lawsuit: Last month, Zillow sued MRED and Compass over an allegedly conspiratorial partnership between the MLS and brokerage to conceal listings from consumers and "punish Zillow for not going along with it."

Zillow claims that after forming an agreement with Compass to display the brokerage's listings nationwide, MRED demanded that Zillow reinstate previously banned Compass listings that violated the portal's listing standards — or risk losing access to the MLS's data feeds.

Zillow trying to 'weaponize the judicial system,' CoStar says: In the amicus brief, attorneys for CoStar — which operates the competing search portal Homes.com — contend that Zillow wants to have it both ways when it comes to listings access.

"Zillow wants a court order forcing MLSs to hand over their listings while Zillow hoards its own exclusive pre-market inventory — a breathtaking 'heads I win, tails you lose' proposition," Gene Boxer, CoStar's general counsel, said in a news release. 

"The Court should see this motion for what it is: An attempt to weaponize the judicial system to entrench Zillow's dominance at the expense of competition, consumers, and the MLS system that has served the industry for decades," Boxer added.

Claims of anti-consumer behavior: In its filing, CoStar specifically calls out Zillow Preview — the portal's pre-market listing program introduced in March — which it characterizes as anti-consumer. CoStar argues that the program "mirrors the exact conduct of which Zillow complains in this case, just on a larger scale."

"Zillow has grown so large that it believes a listing on Zillow's network alone is, by definition, pro-consumer," according to the CoStar brief. "Zillow needs a reality check. In the interests of competition and consumers, the Motion should be denied."

What Zillow had to say: In an email, a Zillow spokesperson defended the portal's Preview product.

"CoStar and Compass are making the same flawed argument: that premarketing and private marketing are the same thing. They are not, and the distinction matters enormously," the spokesperson said. "Zillow Preview is pre-marketing — publicly visible for any buyer to see it, save it and connect with the listing agent directly for free. No buyer is required to work with any specific brokerage to access it."

"Compass Private Exclusives are pay-to-play private marketing. Those listings are hidden from buyers unless they work with a Compass agent. The explicit purpose is to route listings through Compass's own network before — or instead of — making them available to the public. Calling those the same thing is a word game designed to muddy a clear distinction, and it is exactly the kind of conflation that harms buyers and sellers when it goes unchallenged."

How we got here: In April, MRED — which has operated its own private listing network for more than a decade —  announced that it was opening access to all licensed agents nationwide, with Compass International Holdings the first to jump on board. 

MRED CEO Rebecca Jensen acknowledged at the time that the move might create friction with other MLSs, but she emphasized that the MLS has a responsibility to listen to its members — and MRED's members were asking for more options.

While Zillow began enforcing its listing access standards in June 2025, it refrained from doing so in MRED's coverage area due to the MLS's "unique situation" with private listings. 

Zillow had, however, barred some Compass listings that didn't comply with the portal's listing policies, and once the partnership between MRED and Compass was announced, the MLS threatened to cut its feed to Zillow if it didn't reinstate nine banned Compass listings.

That prompted Zillow to file its May 12 lawsuit claiming it was coerced into abandoning its listing standards in Chicagoland. A week later, MRED — which said Zillow was violating the MLS's IDX display rules — followed through on its threat and suspended Zillow's listing feeds, which were restored by an emergency court order on May 22.

This story has been updated with a statement from Zillow.