Section 97F. No city or town shall require a member of its police department, or other employee with police powers, to perform the duties of a firefighter during his tour of duty; provided, however, that nothing in this section shall prohibit any such member from serving as a call or volunteer firefighter, or from responding to an emergency in the normal course of his duties. No police officer, or other employee with police powers, shall, in connection with any industrial or labor dispute, perform the duties of a firefighter or any duties other than those regularly assigned to him.