Breaching anti-money laundering laws and social responsibility protocols entails hefty costs, a lesson that British bookmaker William Hill learned the hard way.

The wagering firm has been fined £6.2 million (US$8.6 million) on charges of turning a blind eye on 10 customers who reportedly managed to deposit dirty money, the UK Gambling Commission (UKGC) said.

It was the biggest fine that the UKGC handed to a gambling operator this year and the second biggest penalty imposed by the agency since it hit betting firm 888 Holdings with a £7.8 million fine in 2017.

Aside from imposing fines, the UKGC also ordered Hills to appoint external auditors to review its anti-money laundering and social responsibility protocols. The UKGC pointed out that Hills “failed to mitigate risks and have sufficient numbers of staff to ensure their anti-money laundering and social responsibility processes were effective.”