The Italian competition watchdog is wading into online booking sights and has its eye on TripAdvisor to see if the influential holiday review website responds appropriately to avoid publishing fake opinions.

The authority is currently investigating Expedia and Booking.com, saying their agreements with hotels may prevent consumers from getting a better deal. In a statement on Tuesday, the watchdog said it had received complaints about TripAdvisor from consumers as well as hotel and restaurant owners.

TripAdvisor is a travel website that gathers readers' reviews of hotels and restaurants. The authority said in a separate document on its website that TripAdvisor may have published opinions of people who had not actually been to the places they rated. The watchdog growled that TripAdvisor may not make it clear enough the distinction between information provided independently by travellers and business profiles that hotels and restaurants pay to get published on the website.

Its investigations into Expedia and Booking.com centred on clauses applied by Booking and Expedia that prevent hotels from offering better prices and conditions through other online services and, generally, any other booking system (including hotels' own websites).

"The authority believes the use of such clauses by the main two platforms on the market may significantly limit competition."

The watchdog said it would conclude the investigation by August 2015.