“Such practices would consist of the coordination of prices and other commercial conditions by real estate intermediaries,” the CNMC watchdog said in a press release.
“This coordination would have been implemented, among other means, through the use of software and computer platforms and would have been facilitated by companies specialized in computer solutions,” it added.
In simple terms, the sites all used linked algorithms to coordinate prices and commissions on both sale and rental properties offered on their sites, a practice which in turn led to pushing up the final cost of the property to the buyer or renter.
It is the first time that such the watchdog had launched proceedings based on use of algorithms to control pricing.
The disciplinary proceedings affect seven companies, including household names familiar to those who have ever attempted online property searches.
The biggest name is that of Idealista SA, the go-to site for those looking to rent or buy property across Spain. Look & Find and Inmovilla are also mentioned.
But Idealista said it “emphatically denies any participation in the investigated practices” and would work closely with the CNMC in its investigation.
Spain has seen a boom in both house sales and rental prices in recent years, where rental prices have soared by 50 percent in the five years leading up to last August, according to a 2019 Bank of Spain report.
Spain's leftwing coalition government led by Pedro Sanchez of the Socialist party (PSOE) have vowed to tackle the issue insisting that guaranteeing the right to decent housing is a top priority.