Recommended Resources 

Professional Ethics in Volunteer Management
The Council for Certification in Volunteer Administration determines the core ethical values and principles for this field, and offers a number of resources for leaders of volunteer engagement and educators  

Engage Journal Articles on Ethics
An active journal with over 20 year of volunteer engagement articles.

Ellis Archive Resources on Ethics
An archive with valued volunteer management resources from the past

Nonprofit Issues: Your Legal Questions Answered
Nonprofit Issues is a nonprofit legal newsletter that has an extensive Q&A section.  Search under "volunteer" and you'll find a range of answers.