So have you never spoken to cabin crew about anything other than "work related" topics in the cruise then ?
Talking about union membership would be a work related topic. I talk about all sorts - work related or not.
However, handing out forms on behalf of an organisation is doing the work of that organisation and a totally different thing.
Nothing wrong with talking about issues but as I said while employed by organisation A it is normal to be excluded during work time from doing the work of organisation B.
When you have a union you will see that time off during working hours for union duties are very much laid down in black and white and subject to agreement.
Regards,
DFC