The brokerage firm argues that Zillow is using its platform dominance to stifle competition and control how agents market homes. Two of the nation’s real estate titans are on a collision course.

Compass says that Zillow is violating antitrust laws by forcing listings onto its platform.In April, Zillow said that it would permanently ban listings that aren't widely available.At issue is whether companies like Compass can post listings online that aren't also on Zillow.