Real estate brokerage company Compass has sued Zillow over its policy to ban private home listings.

In a filing with the U.S. District Court for the Southern District of New York, Compass claims that “Zillow has sought to rely on anticompetitive tactics to protect its monopoly and revenues in violation of the antitrust laws.”

Compass says Zillow has implemented an exclusionary policy that says if a home seller and their real estate agent market their property off Zillow for more than one day, that Zillow and its allies, Redfin and eXp Realty, will ban that home from being listed on their search platforms.

“The Zillow Ban seeks to ensure that all home listings in this country are steered on to its dominant search platform so Zillow can monetize each home listing and protect its monopoly,” Compass said in the lawsuit.

Compass alleges the ban was enacted to prevent rivals from competing against it and reduces homeowner choice.

“In a free and competitive market, competitors’ products and strategies should rise and fall on merit — not the whims of a monopolist gatekeeper like Zillow,” Compass said.

Compass wants an injunction that would prohibit Zillow from implementing and enforcing its ban and implementing and enforcing similar policies. The company also wants a trial by jury and an unspecified amount in damages.

Zillow said Monday it believes the claims in the lawsuit are unfounded and that it will vigorously defend against them.

The housing market has become more fierce of late. Last month the National Association of Realtors reported that sales of previously occupied U.S. homes fell 0.5% in April from March, to a seasonally adjusted annual rate of 4 million units.

Sales of existing homes barely moved in May, with existing home sales up 0.8% from April to a seasonally adjusted annual rate of 4.03 million units, the National Association of Realtors said Monday. High mortgage rates and rising prices made homebuying less affordable.