Well the first point has to be that PPP was a terrible idea in the first place. How they argued that it would provide investment when the reality was that the company was landed with massive debts immediately on sale is beyond me. Sept 11th didn't cause these financial problems, only added to them.
As for using the money for investment... the savings they make will probably just about cover the interest payments on the debt!
I don't think the unions are happy with the idea of a pensions holiday - but when there is no way you can stop it what are you supposed to do?! The only thing the unions could do is to try and get as much as possible in return. Those who negotiate these deals are trained negotiators and so, with respect, are better skilled to deal with this than their ATCO members.
P.S. For those still unsure... The contribution holiday it for TAG/NATS only. Members contributions remain unchanged.