As management have now decided that aspects of a NEW pension are "non-negotiable" perhaps it's time that the union informed management that their repayment of the money owing to the pension fund from their payment holiday is now NON-NEGOTIABLE including interest that would have accrued over the 6/7 years that this money remained unpaid.Then we can look again in 12 months time and see how healthy the pension scheme will then suddenly look.
I know this is a naive outlook but this should be the starting point of ANY union negotiations not immediately suggesting a 2-tier pension scheme straight away as in the union announcement.