Balint Horvath, head of communications at GVH, told Reuters that the raid was conducted as part of a sector inquiry launched by the national competition authority on Aug. 24.

Booking confirmed that GVH visited its office.

"We can confirm that we are fully cooperating with the Hungarian Economic Competition Office, who visited our offices today," the company said in an emailed reply to Reuters questions.

The GVH had launched its broad enquiry in August saying its investigation "will assess whether competition may have been harmed by, among other things, Booking's contracting and contract enforcement practices."

"According to market information received by the GVH, the business of many Hungarian accommodation providers has recently been seriously disrupted by the fact that one of the largest online accommodation platforms - Booking.com - has applied contractual terms and practices to them that it does not apply to other accommodation partners," it said, citing Booking's payment practices.

GVH said it had received 28 complaints about the withholding of accommodation fees, which it said might have affected fair competition between accommodation providers.

(Reporting by Krisztina Than and Boldizsar Gyori; Editing by Alexandra Hudson)