(1) The commission, after hearing upon reasonable notice, shall decide in each application for certification as an exclusive bargaining representative, 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 public employees; the history of collective bargaining by the public employees and their bargaining representatives; the extent of organization among the public employees; and the desire of the public employees. The commission shall determine the bargaining representative by: (a) Examination of organization membership rolls; or (b) conducting an election as provided under RCW 41.56.070 or 41.56.095.

(2) For classified employees of school districts and educational service districts:

(a) Appropriate bargaining units existing on July 24, 2005, may not be divided into more than one unit without the agreement of the public employer and the certified bargaining representative of the unit; and

(b) In making bargaining unit determinations under this section, the commission must consider, in addition to the factors listed in subsection (1) of this section, the avoidance of excessive fragmentation.