30 Tex. Admin. Code § 116.161
The commission may not issue a permit to any new major stationary source or major modification located in an area designated as attainment or unclassifiable, for any National Ambient Air Quality Standard (NAAQS) under FCAA, §107, if ambient air impacts from the proposed source would cause or contribute to a violation of any NAAQS. In order to obtain a permit, the source must reduce the impact of its emissions upon air quality by obtaining sufficient emission reductions to eliminate the predicted exceedances of the NAAQS. A major source or major modification will be considered to cause or contribute to a violation of a NAAQS when the emissions from such source or modification would, at a minimum, exceed the de minimis impact levels specified in § 101.1 of this title (relating to Definitions) at any locality that is designated as nonattainment or is predicted to be nonattainment for the applicable standard.
30 Tex. Admin. Code § 116.161