The UK competition watchdog has opened an investigation into three of the world’s biggest hotel chains – Hilton, InterContinental Hotels (IHG) and Marriott – amid suspicions they could be sharing “competitively sensitive” information with each other.

The Competition and Markets Authority (CMA) is investigating allegations that the businesses, which together operate more than 25,000 hotels worldwide, could be sharing information through the data analytics tool STR. CoStar, the real estate data firm that owns STR, is also under investigation.

While it is common for hotel chains to use data analytics and algorithms to help them set prices, which can improve competition and lower costs, sharing this information with competitors can be harmful to their customers.

The watchdog said: “When rival businesses share competitively sensitive information – including through a third-party data analytics provider – this reduces the uncertainty competing businesses normally have about how each other will act.

“This can affect how strongly companies compete because it makes it easier for them to predict what each other will do and coordinate their behaviour.”

The CMA will spend the next six months gathering information as part of its investigation.

Shares in the FTSE 100-listed IHG dropped by as much as 5% in early trading on Monday.

CoStar, which is headquartered in Washington DC, provides data on the hotel industry’s standard metrics such as occupancy, average daily rates for rooms and revenue per available room. This makes it easier for hotels to determine room charges and match supply with demand.

The CMA said: “At this stage, no assumptions should be made about whether the law has been broken. Following a period of investigation and information gathering, the CMA may issue a statement of objections if it comes to the provisional view that competition law has been infringed.”

A spokesperson for CoStar said it was cooperating with the CMA but that it was “surprised” at the regulator’s interest “in a longstanding hotel data analytics and benchmarking platform, that for decades has been used by companies and government entities alike to better assess market dynamics”.

A spokesperson for IHG, which is headquartered in Windsor, England, and has more than 400,000 staff around the world, said the company would cooperate fully with the CMA’s inquiries.

The regulator said its investigation reflected a wider commitment to ensuring “new technologies” supported fair competition and did not harm consumers. In November, the regulator opened investigations into eight companies about their online pricing practices.

Hilton and Marriott were approached for comment.