Fair Trade Commission then Chairperson Joh Sung-wook speaks during a press conference at the Government Complex Sejong, Jan. 19. Yonhap

Korea's antitrust regulator said Tuesday it has decided to impose fines of 2.5 million won ($1,751) each on two accommodation booking platforms for failing to inform customers of their advertisement-based search results.

The penalty on Booking.com and Agoda, both under the U.S.-based Booking Holdings, came as the platforms arranged search results based on advertisement without properly notifying customers of the deal, according to the Fair Trade Commission (FTC).

Booking.com also placed a "thumbs-up" logo next to hotels that paid fees without informing users of the meaning. Agoda used vague expressions, such as "Agoda Growth Program" or "Agoda Growth Express," on advertised hotels without further explanations as well.

The regulator pointed out the move was "deceiving," as customers were likely to believe certain businesses were placed at the top based on their services and facilities.

"By having online travel agencies provide accurate information on advertised products, customers can make reasonable decisions based on their preferred terms and prices when booking accommodations," the FTC said. (Yonhap)