Why banks do not like FBL and CPBL?

FBL is the short form of Freight Forwarder Bill of Lading or Forwarder's Bill of Lading and CPBL is the short form of Charter Party Bill of Lading.

Banks, especially in letter of credit transactions, do not accept presentation of a FBL instead of a marine bill of lading, unless FBL is signed by the freight forwarder "as carrier" or "as agent on behalf of the carrier"or else presentation of FBL expressly permitted in the letter of credit.

Likewise a CPBL can only be acceptable if letter of credit requests presentation of a Charter Party Bill of Lading.

Today I would like to explain why banks do not accept CPBL or FBL instead of bill of lading.