C.R.S. § 8-3.3-110

(1) The director shall, upon receipt of a petition for a representation election, designate the appropriate bargaining unit for collective bargaining in accordance with this section. The designation must be determined by: (a) Consent of the parties; or (b) If there is not agreement between the parties, an administrative determination of the director. (2) In determining the appropriateness of a bargaining unit, the director shall consider: (a) The desires of the public employees; (b) The similarity of duties, skills, and working conditions of the public employees involved; (c) The wages, hours, and other working conditions of the public employees; (d) The administrative structure and size of the public employer; (e) The history of collective bargaining with that public employer, if any, and with similar public employers; and (f) Other factors that are normally or traditionally taken into consideration in determining the appropriateness of bargaining units in the public sector.