49 CFR § 385.301T - What is a motor carrier required to do before beginning interstate operations?
(a) Before a motor carrier of property or passengers begins interstate operations, it must register with the FMCSA and receive a USDOT number. In addition, for-hire motor carriers must obtain operating authority from FMCSA following the registration procedures described in 49 CFR part 365, unless providing transportation exempt from 49 CFR part 365 registration requirements.
(c) A Mexico-domiciled motor carrier of property or passengers must register with the FMCSA by following the registration procedures described in 49 CFR part 365 or 368, as appropriate. The regulations in this subpart do not apply to Mexico-domiciled carriers.