The FTC alleges the companies violated federal antitrust laws when Zillow paid Redfin $100 million to essentially re-host Zillow multifamily rental listings on Redfin.

The Federal Trade Commission is suing real estate giants Zillow and Redfin, alleging the two illegally conspired to reduce competition in the online multifamily rental listing market, the agency said Tuesday.

In the complaint, the FTC alleges the companies violated federal antitrust laws earlier this year when Zillow paid Redfin $100 million to essentially re-host Zillow multifamily rental listings on Redfin and its sites.