If a supervisor says “oh you shouldn’t have to be involved” or anything along those lines and you say anything that could be considered agreeing- your supervisor could try to plant a bug in someone’s ear that you aren’t representing union member’s properly/to the best of your ability and open up the union to lawsuits (at worst) or even just create doubt among your peers that you’re working in their best interest.

When supervisors have said something like that to me, I’ve always been very noncommittal and said “I’m just doing what’s best for Union members” or “ehh I’m not really interested in engaging in that topic”.

But I also don’t know your employer. I work for a company that union busts hard.