The commissioner shall decide in each case whether in order to assure to employees the fullest freedom in exercising rights guaranteed by this chapter, the unit appropriate for the purposes of collective bargaining is the employer unit, craft unit, plant unit, or subdivision thereof. The commissioner may not:
1. Decide that any unit is appropriate for such purposes if such unit includes both professional employees and employees who are not professional employees unless a majority of such professional employees vote for inclusion in such unit.
2. Decide that any craft unit is inappropriate for such purposes on the ground that a different unit has been established by a prior commissioner determination, unless a majority of the employees in the proposed craft unit vote against separate representation.
3. Decide that any unit is appropriate for such purposes if it includes, together with other employees, any individual employed as a guard to enforce against employees and other persons rules to protect property of the employer or to protect the safety of persons on the employer's premises; but no labor organization may be certified as the representative of employees in a bargaining unit of guards if such organization admits to membership, or is affiliated directly or indirectly with an organization which admits to membership, employees other than guards.
In determining whether a unit is appropriate, the extent to which the employees have organized is not controlling.