Real estate giant Compass is suing Zillow, alleging that the online property website is violating antitrust laws with a new rule that bans home listings from its platform if they appear on any other service for more than 24 hours before being posted on Zillow.

Zillow’s rule, announced by the company in April, took effect on May 28, with the company saying that the new standard is necessary to ensure that listings are “marketed to every buyer” to give house-hunters “fair access to listings without having to get access behind a velvet rope controlled by any one company.”

But Compass, which seeks to give some clients a competitive advantage by posting homes before they appear on Zillow and other sites, is alleging that what it calls the “Zillow ban” violates federal antitrust laws. The real estate company claims that ZIllow is leveraging its market dominance to impose the block on listings outside of its website, and that it is aimed at hobbling competition, according to the lawsuit.