The Hibernian Catholic Benefit Society says more money than previously thought has been taken from one of its bank accounts, taking the amount known to have been removed to more than $1 million.
Accountants last month found that $598,000 had been taken over a number of years from the society's credit union.
The Serious Fraud Office began an investigation into the scale of the fraud.
Society president Mike McBride says further enquiries reveal another amount - also more than $500,000 - had been siphoned over several years from an account used to provide members with benefits such as insurance.
He says the loss will not have an adverse effect on members' benefits, but it is a further shock for them.