The labor relations agency shall decide in each case, in order to assure to employees the fullest freedom in exercising the rights guaranteed by AS 23.40.070 - 23.40.260, the unit appropriate for the purposes of collective bargaining, based on such factors as community of interest, wages, hours, and other working conditions of the employees involved, the history of collective bargaining, and the desires of the employees. Bargaining units shall be as large as is reasonable, and unnecessary fragmenting shall be avoided.