I don't mean any disrepect at all, but it feels to me as if you're looking for reasons to blame the union. Honestly, in this instance for the reasons I've outlined, I don't think you're being very fair.
That's not how it's meant to come across. I think the union are one of four problems in this mess - none of the parties involved in the dispute come out well of it and none appear to really care about the customer. I do struggle to believe that employees need to get a doctors certificate for a single day sick though .... doctors just don't do that and the law allows for 7 days self cert. Now if the unions called a strike over that I'd be fully supportive.