davecr,
...can't discriminate against someone who participates in IA...
I would imagine you are correct that they cannot discriminate between someone who participates in IA and someone who doesn't. Interestingly, the email doesn't make that distinction. It says (I paraphrase)
"if there is a "Yes" vote" not "those who go on strike".
So according to the letter I would suggest ST will be permanently removed from
ALL cabin crew, whether they strike or not if there is a Yes vote.
High stakes.