Yes, that could be a problem however if clear rules were created from the inception of the forums then this could be addressed.
An area for all union members
an area that excludes managers.
In the registration process it is made quite clear than to encourage free communications without the fear of discrimination within the workplace managers would not be permitted to view certain areas/forums.
I would like to think that Virgin and its' managers would be happy with that as it is encouraging communication between members and the union. If they didn't like the idea then they are simply disrupting the communication process and once again people would not feel free to communicate what they really felt without fear of being "watched". This would be a powerful tool for the union and its members and would help ensure it is representing the members views at all times. I do not think this would work if managers were part of it, especially after recent weeks.