Each Workspace has its own group of members. All current members of a Workspace are grouped together in the BSCW group 'Members of <Workspace name>'. You can become a member of a Workspace only by being invited by its owner or by another member who is entitled to invite new members.
A registered user of a BSCW server who is invited to a Workspace on that server will learn this only from the fact that this new Workspace is listed with the 
icon in her 
Folder. There is no additional automatic notification.
Your Daily Workspace Activity Report will also notify you of any new Workspace that you have been invited to on the day before, unless you have excluded Events from the report (which may not be such a good idea).
BSCW does not provide a specific function to decline the invitation to a Workspace. If you do not want to be associated with a particular Workspace, you have to remove yourself from the list of members:
icon next to the Workspace name to display the Workspace's Members page.
to remove yourself from this BSCW group.