Md. Code, State Personnel and Pensions § 30–303

(a) An eligible employee shall elect to:

(1) join a pension or retirement system in accordance with the provisions of this Division II applicable to that system; or

(2) participate in the program.

(b) An eligible employee shall:

(1) make an election under this section in writing; and

(2) file the election with the Board of Trustees and the employing institution at commencement of employment.

(c) An eligible employee’s election under this section is a one–time, irrevocable election.

(d) The effective date of the election shall be the day of commencement of employment.