The letter of credit can also be the source of payment for a transaction, meaning that redeeming the letter of credit will pay an exporter. Letters of credit are used primarily in international trade transactions of significant value, for deals between a supplier in one country and a customer in another. In such cases the International Chamber of Commerce Uniform Customs and Practice for Documentary Credits applies. Almost all letters of credit are irrevocable, i.e., cannot be amended or canceled without prior agreement of the beneficiary, the issuing bank and the confirming bank.