There may be not more than two bargaining units at each public library system including: One bargaining unit for employees; and One bargaining unit for supervisory employees. Except as provided in paragraph (2) of this subsection, a bargaining unit may contain full–time or part–time employees. A bargaining unit may not include volunteers or temporary employees with less than 90 days of service in a 12–month period. This subtitle may not be construed to modify or terminate a bargaining unit that was recognized or in existence on or before June 30, 2024. If an employee organization has been certified under State or local law on or before June 30, 2024, to be an exclusive representative of employees of a public library system, the employer shall accrete all eligible positions into the existing bargaining unit in accordance with this section on request of the exclusive representative. An accretion under this subsection shall be subject to a showing of interest and election by employees in the accreted positions in accordance with the procedures under § 23–907 of this title.