Traditionally, volunteers have not been entitled to sue for harassment under Title VII of the Civil Rights Act, which is the primary federal law protection for employees against discrimination and harassment.  But there have been a few cases in recent years holding that people who volunteer their time without compensation or benefits can be considered “employees” if they work under conditions comparable to terms of employment.  (See Nonprofit Issues®, January 16, 2013.)

I wouldn’t recommend that you start with a lawsuit, however, until you have exhausted your potential remedies with the hospital administration.  I would probably talk first with the manager’s manager.  If that doesn’t help, I would try to get a copy of the hospital’s whistleblower policy.  If the policy is well written to protect the hospital’s interests, it is likely to prohibit retaliation against people, including volunteers, who file complaints in good faith. Even if you didn’t actually file a complaint, the policy might protect you against retaliation from someone who thought you did. In the unlikely event that the hospital doesn’t have a whistleblower protection policy or if the one they have doesn’t cover your situation, I would check your state law to see if it has a statutory whistleblower policy that might be applicable.

If the whistleblower protection approach doesn’t yield any promise, I would ask a lawyer whether there is any likelihood of prevailing in a lawsuit under state or federal employment law, and if so, what the recovery might be.  If you got your old position back, would it be worth the time and cost to prosecute the case against an institution that really doesn’t want your help? 

There must be a lot of organizations in your area that would appreciate the services of a reliable long-term volunteer and not treat you the way the hospital did.