14 CFR § 121.517
Flight time limitations: Other commercial flying: airplanes
July 13, 2020
No airman who is employed by a certificate holder conducting supplemental operations may do any other commercial flying, if that commercial flying plus his flying in operations under this part will exceed any flight time limitation in this part.
[Doc. No. 28154, 61 FR 2613, Jan. 26, 1996]