Tex. Local Government Code § 143.085

(a) If a municipality's governing body adopts an ordinance that vacates or abolishes a fire or police department position, the fire fighter or police officer who holds that position shall be demoted to the position immediately below the vacated or abolished position. If one or more positions of equal rank are vacated or abolished, the fire fighters or police officers who have the least seniority in a position shall be demoted to the position immediately below the vacated or abolished position. If a fire fighter or police officer is demoted 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. If the vacated or abolished position is filled or re-created within one year after the date it was vacated or abolished, the position must be filled from the reinstatement list. Appointments from the reinstatement list shall be made in order of seniority. A person who is not on the list may not be appointed to the position during the one-year period until the reinstatement list is exhausted.

(b) If a position in the lowest classification is abolished or vacated and a fire fighter or police officer must be dismissed from the department, the fire fighter or police officer with the least seniority shall be dismissed. If a fire fighter or police officer is dismissed 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 reinstatement list in order of seniority. Appointments from the reinstatement list shall be made in order of seniority. Until the reinstatement list is exhausted, a person may not be appointed from an eligibility list. When a person has been on a reinstatement list for three years, the person shall be dropped from the list but shall be restored to the list at the request of the commission.