49 U.S.C. § 13901 — Requirements for registration

(a) In general: A person may only provide transportation^* as a motor carrier^* under subchapter I of chapter 135, service as a freight forwarder^* under subchapter III, or service as a broker^* under subchapter I, if that person is registered under this chapter for that specific transportation or service.

(b) Registration Numbers.
(1) In general: If the Secretary^* registers someone to provide transportation or service — as a motor carrier^*, freight forwarder, or broker — the Secretary must give that person a distinct registration number for each type of authority they're registered for.
(2) Transportation or service type indicator: Each registration number must show what kind of transportation or service it covers, including whether it's for a motor carrier, freight forwarder, or broker.

(c) Specification of Authority: For every agreement to provide transportation or service that needs registration under this chapter, the registrant must state^* in writing what authority they're relying on to provide it.