A Motor Carrier (MC) number is a unique identifier assigned by the Federal Motor Carrier Safety Administration (FMCSA) to commercial motor vehicles that transport regulated commodities for hire in interstate commerce. It is also referred to as operating authority and is required in addition to a DOT number for companies that operate as for-hire carriers, transport passengers or arrange for their transport in interstate commerce, or transport federally regulated commodities or arrange for their transport in interstate commerce. The FMCSA operating authority is often identified as an "MC," "FF," or "MX" number, depending on the type of authority that is granted.

The MC number dictates the type of operation a company may run and the cargo it may carry, and it also determines the level of insurance/financial responsibilities a company must maintain. Unlike the USDOT Number application process, a company may need to obtain multiple operating authorities to support its planned business operations.

Private carriers (carriers that transport their own cargo), "for-hire" carriers that exclusively haul exempt commodities, and carriers that operate exclusively within a federally designated "commercial zone" that is exempt from interstate authority rules are not required to have operating authority.

To obtain an MC number, companies must register with the FMCSA through the Unified Registration System (URS) . The application process involves completing an application and paying a fee via credit card or check.