The UK’s competition watchdog is going to open an investigation into online hotel booking platforms amid concerns surrounding the “clarity, accuracy and presentation of information” on their websites.

About 70 percent of people researching hotels last year used booking sites, which include Trivago, booking.com, Expedia and Late Rooms.

According to Booking.com, which employs more than 15,000 employees across 204 offices worldwide, “1,500,000 room nights are reserved” every day on its platform.

In the third quarter to 30 September, Expedia, which claims to be the largest online travel provider in the UK, recorded a rise of 11 percent in its revenue to $22.2bn.

In a statement, Trivago, which is majority owned by Expedia, said:

Trivago will work with the CMA to explain the benefits it delivers to consumers looking for their ideal hotel.

The CMA will examine whether hotel websites are guilty of levying hidden charges, manipulating search results, making misleading discount claims or engaging in pressure selling.

Another area of concern is the extent to which sites guide customers towards particular hotels based on the amount of commission they earn from a booking.

Nisha Arora, a senior director at the CMA, told the BBC’s Today programme:

We are concerned about the clarity and accuracy of these sites. Rather than helping consumers they may actually be making it more difficult for them. When you put in your criteria — which room you want, when you want to stay — they are listed in a certain order. This is not just influenced by consumer preference but by commission – commercial considerations – and consumers might not be aware of this.

The CMA is asking hotel booking websites to provide “information to understand more about their practices.”

The watchdog is also calling on customers who use the booking websites as well as the hotels that advertise with them to share their experiences.

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In a statement an Expedia spokesperson said:

Expedia has been informed of the CMA’s review to better understand the hotel booking sector. We welcome further discussion with the CMA to review how platforms provide transparency to the market increasing competition between hotels and to increase consumer benefit.

Booking.com declined to comment on the CMA’s investigation.