40 CFR § 61.17
State authority
June 9, 2020
(a) This part shall not be construed to preclude any State or political subdivision thereof from—
(1) Adopting and enforcing any emission limiting regulation applicable to a stationary source, provided that such emission limiting regulation is not less stringent than the standards prescribed under this part; or
(2) Requiring the owner or operator of a stationary source to obtain permits, licenses, or approvals prior to initiating construction, modification, or operation of the source.
[50 FR 46294, Nov. 7, 1985]