(1) The Employment Relations Board shall decide in each case whether the unit appropriate for the purposes of collective bargaining is the employer unit, craft unit, plant unit, or subdivision thereof. However, the board shall not decide that:
(a) A unit is appropriate for such purposes if the unit includes both professional employees and employees who are not professional employees, unless a majority of the professional employees vote for inclusion in the unit;
(b) A craft unit is inappropriate for such purposes on the ground that a different unit has been established by a prior determination of the board unless a majority of the employees in the proposed craft unit vote against separate representation; or
(c) A unit is appropriate for such purposes if it includes, together with other employees, an 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 employers premises. However, no labor organization shall 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.
(2) In determining whether a unit is appropriate for the purposes specified in subsection (1) of this section, the extent to which the employees have organized is not controlling. [Formerly 662.545]