NEW YORK (Reuters) -Zillow ( ZG ) was sued on Wednesday by Homes.com owner CoStar Group ( CSGP ), which accused the largest U.S. online real estate portal of publishing at least 46,979 copyrighted photos without permission.

The complaint filed in Manhattan federal court seeks unspecified compensatory and punitive damages, which Arlington, Virginia-based CoStar ( CSGP ) estimated could exceed $1 billion.

CoStar ( CSGP ), whose real estate listing websites also include Apartments.com and LoopNet.com, accused Seattle-based Zillow ( ZG ) of exploiting the photos, many of which contain watermarks, to boost its rental listings business.

Zillow ( ZG ) did not immediately respond to requests for comment.

According to the complaint, Zillow ( ZG ) uses CoStar's ( CSGP ) photos to induce property managers and landlords to "claim" properties that are not actively listed for rent, and then sells advertising packages and tools to generate revenue.

CoStar ( CSGP ) said Zillow ( ZG ) also distributes some photos under syndication agreements to rival portals Realtor.com and Redfin, owned respectively by News Corp and Rocket Cos.

Zillow's ( ZG ) "free-riding" on the photos results in infringement "on a massive scale, however measured," CoStar ( CSGP ) said.

CoStar ( CSGP ) said it provides limited licenses of its photos to real estate professionals and does not allow sublicensing.

In 2019, CoStar ( CSGP ) obtained a $500 million judgment against the bankruptcy estate of real estate listing platform Xceligent over the publication of 38,489 copyrighted photos, court records show. Xceligent had filed to liquidate two years earlier.

CoStar ( CSGP ) threatened to sue Realtor.com and Redfin if they do not remove its copyrighted photos.

Realtor.com and Redfin declined to comment. CoStar ( CSGP ) did not immediately respond to a request for additional comment.

In June, Compass, the largest U.S. residential real estate brokerage by sales volume, sued Zillow ( ZG ) for allegedly trying to monopolize private home listings, violating federal antitrust law. Zillow ( ZG ) has called Compass' claims unfounded.

The case is CoStar Group Inc ( CSGP ) et al v Zillow Group Inc ( ZG ) et al, U.S. District Court, Southern District of New York, No. 25-06248.