N.D. Cent. Code § 22-01-14

A continuing guaranty may be revoked at any time by the guarantor in respect to future transactions unless there is a continuing consideration as to such transactions which the guarantor does not renounce. If the contract of guaranty signed by the guarantor so states, the revocation must be in writing and delivered to the guarantee. If the contract does not so state, an oral attempt to revoke is not effective if at the time of the oral communication the guarantee requests delivery of a written revocation and confirms the request in writing.