In this subsection the following words have the meanings indicated. “Confidential employee” means an employee who assists or acts in a confidential capacity with respect to an individual who formulates, determines, or implements management policies in the field of labor–management relations. “Probationary employee” means a Commission merit system employee during the employee’s initial probationary period after hiring. The rights granted to Commission merit system employees under this subtitle do not apply to: attorneys in the Office of the General Counsel; confidential employees; probationary employees; employees in the Office of the General Manager; employees in the Office of the Inspector General; employees in the Office of the Secretary; or supervisors, as defined in § 2(11) of the National Labor Relations Act, 29 U.S.C. § 152(11). Commission employees are divided into five bargaining units consisting of: an office unit that includes: office classification titles in which employees are responsible for internal and external communications, recording and retrieving information, and paperwork required in an office; paraprofessional classification titles in which employees perform, in a supportive role, some of the duties of a professional or a technician but that usually require less formal training or experience than those duties performed by those with professional or technical status; and all other nonprofessional job titles currently unrepresented by any other union; a professional unit that includes professional classification titles in which employees have special or theoretical knowledge that is usually acquired through college training or other training that provides comparable knowledge or work experience; a service, labor, and trade unit that includes: classification titles in which employees: perform service and maintenance; may operate specialized machinery or heavy equipment; and have duties that contribute to the comfort and convenience of the public or to the upkeep and care of Commission buildings, facilities, or grounds; classification titles in which employees are required to have a special manual skill and thorough knowledge of processes that are required through on–the–job training, experience, apprenticeship, or other formal training programs; and classification titles included in the service, labor, and trade bargaining unit as constituted on January 1, 2003; a law enforcement unit that includes Commission police officers; and a technical unit that includes technical classification titles in which employees have a combination of basic scientific or technical knowledge and manual skill that is usually acquired through specialized postsecondary school education or through equivalent on–the–job training. If a single employee organization is certified to represent more than one bargaining unit, the Commission shall negotiate a single contract with that organization covering all employees the organization represents.