For the purpose of this section, a supervisor or supervisory employee shall be an employee who regularly supervises the work of two or more employees and whose work customarily and regularly involves spending more than 50 percent of work time on supervisory, rather than journeyperson, activity. Classifications and positions meeting this definition are documented on a separate listing, additions to or deletions from this list during the term of this Memorandum of Understanding shall be by mutual agreement of the parties. Supervisors as defined above shall not be subject to the provisions of this Section 2.1, Agency Shop, but shall continue to be covered by Section 2.3, Maintenance of Membership.