The UK’s competition watchdog has launched a probe into whether online gambling sites are breaking the law via misleading promotions.

On Friday, the Competition and Markets Authority (CMA) announcing an investigation of “potential breaches of consumer law, including misleading promotions and unfair terms, being used by firms to block players’ payouts.” The CMA said it was prompted to act after the UK Gambling Commission (UKGC) raised similar concerns.

Nisha Arora, the CMA’s senior director for consumer enforcement, said the CMA was “worried players are losing out because gambling sites are making it too difficult for them to understand the terms on which they’re playing, and may not be giving them a fair deal.” Arora said the CMA would work closely with the UKGC during its investigation.

The UKGC’s CEO Sarah Harrison said she had concerns that betting operators’ terms and conditions “appear to bamboozle rather than help the customer make informed choices.” Harrison said too many of the UK’s estimated 5.5m online gamblers felt like “the deck is stacked against them because of an obscure condition that they did not properly understand.”