The Commonwealth Bank of Australia is severing its relationship with mortgage brokers who fail to sign up enough customers to their home loans.

In a letter seen by Fairfax Media, the bank told 'inactive' brokers their accreditation with the lender had expired, effective in 14 days, due to them "not been active with Commonwealth Bank for some time".

"This means you will no longer be able to submit home loan applications to the Commonwealth Bank," the letter, dated February 20, said.

The bank said the move was part of a monitoring program "to ensure that [brokers] comply with our accreditation requirements and that they remain active as Commonwealth Bank Brokers".