Terminal Server shut down button

Hi, I have Windows NT 4 Terminal Server. At the logon window (where to put the username and password) there is the “Shutdown” button that is enabled for everyone who log on this server. So it is possible to everybody to shutdown this computer. I looked in system policies but I did not find the place to disable this button. May be its in the registry. If you know how to disable the “shutdown” button in the logon window, please tell me.

Thank you