Well the back pay has gone if we say shove it, after tax there isn't that much anyway.
Why do you think this is the case? You must have been listening to the Fed Exec rubbish. They've been running around the country telling everyone this but you can have a look at our last EBA
The parties agree to commence negotiations on a new collective enterprise agreement no later than three months prior to the expiry date of this Agreement. The parties are committed to complete negotiations on the new agreement prior to the expiry of this Agreement. Qantas will continue to apply the terms of this Agreement to all employees covered by it until the new agreement takes legal effect. The operative date of the new agreement will be the first pay period on or after 1 January 2005.
The only way you could lose the backpay is if the union agree to allow Qantas to breach the terms of your last EBA. They can't do it legally. Don't listen to the lies from the front table. Just vote no and ask for a new negotiating team.