Shares of online betting operator 888 Holdings Plc. tumbled on Monday after the company announces that it is now under investigation by the UK Gambling Commission (UKGC).

888 shares fell as much as 10 percent – the most since June 2016 on an intraday basis – as spooked shareholders try to cash in on the gains they had before the investigations started.

The Gibraltar-based firm announced on Monday that the UKGC is conducting a review over its compliance with rules to prevent problem gambling.

In a statement, 888 Holdings said it would work with the UKGC on the review.