Portugal Colonial - Spain watchdog fines Booking.com 413 mn euros 

"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 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 spokeswoman for the authority told AFP.

The CNMC 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 percent and 90 percent.

Booking.com, 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 percent.

In May, the European Union added the travel agency 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 (GVH) 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.

N.Esteves--PC