As a Level 3 Member Plus, one of the enforcement privileges available is the /mute60 command. This command allows you to mute a particular user, Voobly-wide, for a period up to an hour. To use this command you would use it as any other force privilege.
e.g. /mute60 Bill
Issuing that command would prevent a user named Bill from talking in any of the lobbies of Voobly. Users who are muted could still use Voobly messenger, and muted users can still play games on Voobly.