[rhelv6-list] how to remove 'shot down' from system menu?

[Alois Treindl]

I have recently installed RHEL6 with GNOME desktop.

In each user's menu appeasr under the entry 'System' also to item 'Shut 
down'

I would like to remove this item for all users except root.
In fact normal users can use this link to shut down the system, they are 
not asked for root password. I do not know how this can happen?
Where can I at least configure that they are asked the root password for 
shutdown?