A carrier may withhold cargo if the sender does not pay for the transporting of that cargo. This is in order to insure that the carrier receives payment for their services.
A carrier lien is a way for transportation services to protect themselves from not being paid for their services by retaining the goods that are be transported if they do not receive payment. However, private carriers are not able to use a carrier lien, unless it is laid out in the contract. Also, if a carrier holds cargo, it is responsible for protecting the cargo from damage and taking all necessary precautions. Overall, carriers are able to insure payment for their services by withholding cargo that has not been paid for.