The source of Compass’ complaint, which was filed on Monday in a New York federal court, is a new rule from Zillow stating that any home listing publicly marketed to consumers anywhere must be published on Zillow within one day or it won’t be allowed to be published on Zillow at all.

Compass is suing Zillow over what it calls the "Zillow ban," a new rule that the real estate brokerage firm claims is meant to control home listings and crush the home search competition.