Joining of thief guilds is now limited to one guild (Galadon, Hamsah, Ruined City, Blackclaw, Dagdan). See GUILD JOIN. Those who have joined multiple guilds will have their membership revoked from all but one.

You will only be blocked from entering those guilds once you have begun learning specialized thief skills, if you have not paid the dues.

You will still be able to freely enter the lesser thief guilds around the land (Hillcrest, Arial City, etc).