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.

Real estate company Compass claims Zillow is illegally undermining competition by banning property listings if they don't appear on Zillow within 24 hours.