Restrict Telnet users

I administer a RS6000 box with AIX 4.3 most of my users login through thier Com ports or Terminal connected to a Ran box. Basicly they are connected to a port by thier cable conected to thier com port. I have some users that Telnet in through the Ethernet network. On all the PC’s we are using a terminal emulator, the only difference is that some go over the Ethernet instaed of the cable conected to thier com port. I can disable the ports for the users that direct connect but I need to know How I can disable the Telnet users. When I do maintenace on the server and I disable to tty ports the Telnet users can still log in.