Spain's competition authority announced on Tuesday it had imposed a record fine of 413 million euros ($448 million) on the online travel agency Booking.com for "abusing its dominant position" over the past five years.
"These practices have affected hotels located in Spain and other online travel agencies that compete with the platform. Its terms and conditions create an inequitable imbalance in the commercial relationship with hotels located in Spain," the watchdog, known by its acronym CNMC, said in a statement.
"By better positioning hotels with more bookings on Booking.com, other online agencies have been prevented from entering the market or expanding," it added.
This is the largest fine ever imposed by the CNMC, a spokesperson for the authority told Agence France-Presse (AFP).
The regulator said Booking.com's market share in Spain, the world's second most visited country after France, during the period under investigation was between 70% and 90%.
Booking.com said it "strongly disagreed" with the CNMC's findings.
The platform said it would appeal the authority's "unprecedented decision," adding that it did not take into account programs it offers its "accommodation partners" to help them boost their business.
The online travel agency, whose parent company Booking Holdings is headquartered in the United States, is a dominant player with a market share in Europe of more than 60%.
In May, the European Union added Booking.com to its list of digital companies big enough to fall under tougher competition rules, giving the firm six months to prepare for compliance with the landmark Digital Markets Act (DMA).
The rules aim to level the playing field in the digital market, ensuring EU users have more options when choosing products.
Brussels said that tougher regulation of Booking.com would mean that holidaymakers would "start benefiting from more choice" and hotels would "have more business opportunities."
Hungary's competition watchdog earlier this month slapped Booking.com with a second fine for failing to cease its "unfair" business practices, including putting psychological pressure on customers.
In 2020, the firm was fined 2.5 billion forint ($7 million) by the Hungarian Competition Authority for aggressive sales tactics.
And on July 15, the authority hit Booking.com with an additional penalty of 382.5 million forint after a follow-up investigation showed the company had continued its unfair practices.