Proper use of InviteAction for a social group

I sent an earlier question, please forgive me for being a bundle of
inquisitiveness today :)

The InviteAction adds a sole property to CommunicateAction: event, defined
as "Upcoming or past event associated with this place, organization, or
action".

How would I use Schema.org properly for an invitation to a social group,
like a Facebook Group or a Meetup group (that in turn has events, but you
must be a member of the group first)?

Thanks,

Kevin