(a) A municipality in this state that is located on the border between this state and the Republic of Mexico may make a mutual fire-protection agreement with its corresponding border municipality in the Republic of Mexico.
(b) Any fire fighter from a border municipality in this state who responds to a call for fire-fighting assistance from the corresponding border municipality in the Republic of Mexico under the terms of an agreement authorized by this section is performing the fire fighter’s official duty for the purposes of Article III, § 51-d, of the Texas Constitution.