(a) Except as provided by Subsection (b), the governing body of a participating department may, at any time, make an election to include all persons who provide support services for the department as members of the pension system. An election under this section takes effect on the first day of the calendar month that begins after the month in which the election is made and communicated to the executive director. Once made, an election under this section is irrevocable.
(b) If a participating department has, before September 1, 2009, enrolled persons who perform support services for the department as members of the pension system, all persons who perform those services for the department are members of the system.

(c) After an election under this section, a participating department that previously did not enroll its support staff as members of the pension system may purchase service credit for service performed before the date of the election under the terms required for prior service credit for service before departmental participation under Section 863.004.