Sens. Cory Booker and Elizabeth Warren asked the Federal Trade Commission last week to probe "anticompetitive and deceptive" practices they say are worsening the housing affordability crisis. The letter targets "dominant real estate actors," but heavily alludes to Zillow and its oft-scrutinized conduct.

"Platform-affiliated agents are frequently required to route buyers to platform-affiliated mortgage lenders who charge higher rates and impose worse loan terms," the letter read. The senators added that neither the platform nor affiliated agents disclose these mortgage referral fees to buyers.

The sides reached a deal in August, requiring Redfin to re-list apartment listings and make investments to compete in the listing space.

The senators cited the national median home price reaching an all-time high of around $440,600 this summer, according to NAR. They also asked the FTC to investigate undisclosed commission-sharing arrangements and the "anticompetitive" use of private listings.