I would suggest it's a bit of both, it takes two to have a disagreement. The Unions have decided to Ballot, It's actually Management and Unions who are collectively responsible, and funnily enough none of them are ever out of pocket, so it's easy to play Mexican standoff when it's not your Bank Balance.
I agree that poor Management leads to Strikes, but Unions painting a picture of significant gains in remuneration that are unreasonable/unachieveable, drive the behaviours of Union Membership.