Tex. Local Government Code § 143.072

(a) On written application of a fire fighter or police officer, the commission shall grant the person a military leave of absence without pay, subject to Section 143.075, to enable the person to enter a branch of the United States military service. The leave of absence may not exceed the period of compulsory military service or the basic minimum enlistment period for the branch of service the fire fighter or police officer enters.

(b) The commission shall grant to a fire fighter or police officer a leave of absence for initial training or annual duty in the military reserves or the national guard.

(c) While a fire fighter or police officer who received a military leave of absence serves in the military, the commission shall fill the person's position in the department in accordance with this chapter.

(d) On termination of active military service, a fire fighter or police officer who received a military leave of absence under this section is entitled to be reinstated to the position that the person held in the department at the time the leave of absence was granted if the person:

(1) receives an honorable discharge;

(2) remains physically and mentally fit to discharge the duties of that position; and

(3) makes an application for reinstatement within 90 days after the date the person is discharged from military service.

(e) On reinstatement, the fire fighter or police officer shall receive full seniority credit for the time spent in the military service.

(f) If the reinstatement of a fire fighter or police officer who received a military leave of absence causes a surplus in the rank to which the fire fighter or police officer was reinstated, the fire fighter or police officer who has the least seniority in the position shall be returned to the position immediately below the position to which the returning fire fighter or police officer was reinstated. If a fire fighter or police officer is returned to a lower position in grade or compensation under this subsection without charges being filed against the person for violation of civil service rules, the fire fighter or police officer shall be placed on a position reinstatement list in order of seniority. Appointments from the reinstatement list shall be made in order of seniority. A person who is not on the reinstatement list may not be appointed to a position to which the list applies until the list is exhausted.

(g) If a fire fighter or police officer employed by a municipality is called to active military duty for any period, the employing municipality must continue to maintain any health, dental, or life insurance coverage and any health or dental benefits coverage that the fire fighter or police officer received through the municipality on the date the fire fighter or police officer was called to active military duty until the municipality receives written instructions from the fire fighter or police officer to change or discontinue the coverage.

(h) In addition to other procedures prescribed by this section, a fire fighter or police officer may, without restriction as to the amount of time, voluntarily substitute for a fire fighter or police officer described by Sections 143.075(b)(1) and (2) who has been called to active federal military duty for a period expected to last 12 months or longer. A fire fighter or police officer who voluntarily substitutes under this subsection must be qualified to perform the duties of the absent fire fighter or police officer.