My reading of it is that the TU want the 2% paid right away... probably because they feel NATS wont want to go as far as to actually take it back as part of any 're-negotiation'.
My assumption is that this will pass a vote with ease and the 2% will be in June pay. A supplementary will be planned in time for September pay (in the event we end up getting more than 2%) or it will be back to the negotiating table if it's required.