Have whomever is responsible for the physical wiring of their ethernet connections remove the cable from the switch.
It's not enough to go to their desks and take their ethernet cables. Pull their access from futher up the chain.
If they are able to get back online and persist, then
1) Set up their systems to a static IP (assuming they're using DHCP)
2) Lock down their systems so that they cannot change their IP settings
3) Block access from these IP addresses from the rest of the network.
That'll get their attention, and hopefully they'll resolve it.
Misery is not my friend, but I\'ll break before I bend.