The commission, upon proper application for certification as an exclusive bargaining representative or upon petition for change of unit definition by the employer or any employee organization within the time limits specified in RCW
41.59.070(3), and after hearing upon reasonable notice, shall determine the unit appropriate for the purpose of collective bargaining. In determining, modifying or combining the bargaining unit, the commission shall consider the duties, skills, and working conditions of the educational employees; the history of collective bargaining; the extent of organization among the educational employees; and the desire of the educational employees; except that:
(1) A unit including nonsupervisory educational employees shall not be considered appropriate unless it includes all such nonsupervisory educational employees of the employer; and
(2) A unit that includes only supervisors may be considered appropriate if a majority of the employees in such category indicate by vote that they desire to be included in such a unit; and
(3) A unit that includes only principals and assistant principals may be considered appropriate if a majority of such employees indicate by vote that they desire to be included in such a unit; and
(4) A unit that includes both principals and assistant principals and other supervisory employees may be considered appropriate if a majority of the employees in each category indicate by vote that they desire to be included in such a unit; and
(5) A unit that includes supervisors and/or principals and assistant principals and nonsupervisory educational employees may be considered appropriate if a majority of the employees in each category indicate by vote that they desire to be included in such a unit; and
(6) A unit that includes only employees in vocational-technical institutes or occupational skill centers may be considered to constitute an appropriate bargaining unit if the history of bargaining in any such school district so justifies; and
(7) Notwithstanding the definition of collective bargaining, a unit that contains only supervisors and/or principals and assistant principals shall be limited in scope of bargaining to compensation, hours of work, and the number of days of work in the annual employment contracts; and
(8) The bargaining unit of certificated employees of school districts, educational service districts, or institutions of higher education that are education providers under chapter
28A.193 RCW must be limited to the employees working as education providers to juveniles in each adult correctional facility maintained by the department of corrections and must be separate from other bargaining units in school districts, educational service districts, or institutions of higher education.