Texas Local Government Code - LOC GOV'T § 143.111. Temporary Duties in Higher Classification

(a) The department head may designate a person from the next lower classification to temporarily fill a position in a higher classification. The designated person is entitled to the base salary of the higher position plus the person's own longevity pay during the time the person performs the duties. Any person who is required to act in a position of higher classification in an emergency situation shall be paid the base salary of the higher position plus the person's own longevity pay for the entire shift without respect to whether an emergency occurs on any particular shift of duty.

(b) The temporary performance of the duties of a higher position by a person who has not been promoted as prescribed by this chapter may not be construed as a promotion of the person.