Md. Code, Educ. § 9-108

(a) Employees of a public charter school: (1) Are public school employees, as defined in §§ 6–401(e) and 6–501(g) of this article; (2) Are employees of a public school employer, as defined in §§ 6–401(f) and 6–501(h) of this article, in the county in which the public charter school is located; and (3) Shall have the rights granted under Title 6, Subtitles 4 and 5 of this article. (b) If a collective bargaining agreement under Title 6, Subtitle 4 or Subtitle 5 of this article is already in existence in the county where a public charter school is located, the employee organization, public school employer, and the public charter school may mutually agree to negotiate amendments to the existing agreement to address the needs of the particular public charter school, including amendments to work days, work hours, school year, procedures for transfers that are consistent with the instructional mission of the school, and extra duty assignments.