Tex. Government Code § 852.101: GENERAL MEMBERSHIP REQUIREMENT.

(a) Except as otherwise provided by this subchapter, a person who is not a member becomes a member of the retirement system if:

(1) on the date a municipal department's participation in the retirement system becomes effective, the person is an employee of the department;

(2) after August 31, 1987, the person becomes an employee of a participating department; or

(3) the person on August 31, 1987, is an employee of a participating department but is not a member because at the time of employment the person's age exceeded the maximum age for becoming a member.

(b) Any person to whom Subsection (a)(1) applies becomes a member of the retirement system on the date the department's participation becomes effective, and any person to whom Subsection (a)(2) applies becomes a member of the retirement system on the date the person is employed. A person to whom Subsection (a)(3) applies becomes a member of the retirement system on September 1, 1987.

Acts 1981, 67th Leg., p. 1876, ch. 453, Sec. 1, eff. Sept. 1, 1981. Amended by Acts 1987, 70th Leg., ch. 183, Sec. 3, eff. Aug. 31, 1987. Renumbered from Vernon's Ann.Civ.St. Title 110B, Sec. 62.101 and amended by Acts 1989, 71st Leg., ch. 179, Sec. 1, eff. Sept. 1, 1989.