Here is our departmental policy:

Former Employees as Volunteers

A.    The hospital accepts the services of its former employees as volunteers.  Former employees may include those who have retired from the organization and those who have left the organization to take employment else where (case by case consideration is given).

B.     To be considered for the volunteer program the former employee must have left the organization in good standing. 

C.     Former employees are not permitted to volunteer within their former department unless the volunteer work is outside the scope of the work for which they were previously paid.

We generally don't let former employees return to a previous department for at least six months, if not longer. Definitely too much of a temptation to step back into former duties. 

Hi Chris

It may also depend if your organization is non-profit.  I found the following google search to be helpful:  

 Fair Labor Standards Act (FLSA) for non-profit organizations

Hi everyone, I have a current employee, that may be resigning their current position in one of our gift shops. they would like to stay involved and asked if they could come back as a volunteer in that same shop. My question is, is this permissible? Labor laws? thoughts!? thanks ALL!