Query on a subform

I have a form that displays an outing for members to sign up. There is
a subform where I display the members of the organization (via a combo
box), using a query to pull the current members.

Now the users would like to only show members by program. So I was
hoping to use the ProgramID field from the form to match against the
ProgramID on the member records in the subform's query. Is this
possible to talk back and forth from the form to the subform's query?
How would I do this?

Thanks

Jeff