Having had several checks collected from me by (typically)
utility companies in order to set up automated
payments (where the company withdraws funds instead of my initiating a
payment each month), I always gave them a blank pre-printed deposit slip with the bank
routing number and personal account imprinted on it in magnetic ink.
For example, if you provided your
utility company with your
routing and account number and authorized them to automatically debit your account for your monthly
payment, it's done via ACH.