Section 2. Employees shall have the right of self-organization and the right to form, join, or assist any employee organization for the purpose of bargaining collectively through representatives of their own choosing on questions of wages, hours, and other terms and conditions of employment, and to engage in lawful, concerted activities for the purpose of collective bargaining or other mutual aid or protection, free from interference, restraint, or coercion. An employee shall have the right to refrain from any or all of such activities, except to the extent of making such payment of service fees to an exclusive representative as provided in section twelve.