ssh is only for remote logins. The local logins do not use it, by default.
In fact, even for remote logins you have to specify ssh ie
Of course you can do that from the local console, but that would be very unusual.
To disable a user's acct, either temporarily or permanently, see http://www.networkdictionary.com/software/Linux325.php
Incidentally, there are a lot of bot scripts trying to brute force root logins via ssh, so best to set
in /etc/ssh/sshd_config and restart sshd:
service sshd restart