Charities are being urged to be on their guard against fraudsters pretending to be their chief executive.
A commission statement said: "Action Fraud, the UK’s national fraud reporting centre, has reported an increase in this type of fraud."
It warned that fraudsters can set up a spoof email account similar to that of the person being impersonated and ask for money to be transferred.
Criminals call a charity pretending to be the chief executive, sometimes when the latter is on leave. A second call by someone posing as a lawyer or regulator might follow.
The commission has advised charities to review their internal procedures for requesting and improving transactions, check email addresses and telephone numbers and be wary of posting sensitive personal information that could be used by fraudsters.
Anyone falling victim to this type of fraud should log a serious incident with the commission and report it to Action Fraud, the regulator added.