Almost two-thirds of Irish charities claim their fundraising has been affected by the negative publicity surrounding Rehab and the CRC.
Of the 297 charities surveyed in April - half say that since November 2013, their fundraising has fallen by up to 10%.
The research, carried out by The Wheel, shows that 61% reported a negative effect, with 36% forced to cut back or suspend services in the past year.
Deirdre Garvey, chief executive of the group - whose conference gets underway in Dublin today - says charities are taking major steps to increase transparency and strengthen governance to rebuild trust.
"There's a variety of different things that charities are doing," she said.
"They're adopting the corporate governance code for community and voluntary charity organisations, they're publishing their accounts online, they're telling their annual reports in easy-to-use language and putting them online.
"It is evermore important that more and more organisations understand that the culture of openness is here to stay because that's the only thing that rebuilds trust."