Taking Domain Control Back from the Registrar?

Patrick Clinger asks: "I run a large community Web site, and today I woke up to find that one of my domain names (proboards21.com) was disabled by my unnamed registrar -- my name servers were changed to NS1/NS2.SUSPENDED-FOR.SPAM-AND-ABUSE.COM and I no longer have access to that domain in my control panel. I am in no way involved in any spam activities, and the registration for my domain expires in 2007. I would expect at least a courtesy call or an email letting me know what happened, but neither was provided by the unnamed registrar. What can you do when suddenly a registrar goes off and takes control of your domain when there was no violation of your agreement with them? What is to prevent any registrar from taking over any domain when they feel like it? Right now my domain is in limbo, waiting for them to hopefully restore it to the correct name servers."