The union is trying to look after their members, that's what they're there for. I'm no union loving lefty, far from it, but terms and conditions are collapsing across the industry. At some point, enough is enough. Working with substantially less manpower on each flight may be legal, but that's 20% less than the competition use so we'd be the first to whine about service levels no doubt.
I think we've cut the fat of the former nationalised company, now, as people tend to do, they're taking it too far.