90 Days...
I am guessing the refrence is to the 90 Days notice that ANY employer can serve to their employees with regard to ammendments/termination of current contracts of employment.
Therefore, if BASSA announce a strike date next week you can bet BA will have those letters in the post the next day.
New Fleet could well be here before the end of the current season. As far as I know, if you don't accept the new T&Cs you are deemed to have resigned.
As with many other contributors, I am not a legal expert and am happy to be proved wrong.