Suspend Client Account in WHM
From Lunarpages Web Hosting Wiki
To suspend a client account, log into your Webmaster Reseller WHM, then Account Functions > Suspend/Unsuspend an Account. You can scroll either through the list of domain names, or usernames. Click your mouse on one, then enter a reason in the box before clicking the button to suspend the account.
Suspended accounts will be highlighted in red.
Suspending an account will disable it completely, including FTP, logging into Cpanel, email accounts, and also viewing the web site.
To unsuspend an account, click either the domain or user and then the unsuspend button.