More than half of nonprofit executives say they have observed unethical fund-raising behavior, a new study has found. The most common concern raised by the executives: use of percentage-based compensation to pay fund raisers.

The research, released on Monday at the annual meeting of the Association of Fundraising Professionals, was conducted by the Giving Institute, an organization in Glenview, Ill., that represents fund-raising consulting firms. The institute surveyed nearly 450 nonprofit executives in charitable organizations of all types; a majority of those surveyed said they had at least 20 years of experience at nonprofit groups.

While the association has long banned commissions as part of its ethics code, the practice appears to be alive and well, according to the nonprofit executives surveyed. Fund raisers who oppose commissions say they worry that donors will think they are being asked to give more to benefit the fund raiser rather than the charitable cause. —Holly Hall